No problem KB,

I know how you feel, it's hard to translate this type of thing into words that make sense.

The "shelf" is generically called a safety ledge. At some point designers had an idea that if some one fell in the deep end (that couldn't swim), the ledge would give them the ability to "stand", and orientate themselves.

What happened more often was, adventurous children used it for venturing out from the shallow end, using it like a sort of cat walk. They ended up being more trouble then they were worth.

Vinyl comes in rolls that contain a wall pattern, tile at the top, and a pattern below it, in several common wall heights. 42", 40" and so on. What happens when there is a safety ledge (shelf), is the additional volume of the the triangle that makes up this area is added to the calculation of what the deep end would be with out it. They figure out the bottom as if it wasn't there, then add extra liner, minus a bit for a tight fit. That's the simple version of how they do it. The ever decreasing deep end angles is all done on CAD machines, and some how they add the volume of the this shelf into the those numbers. The CAD program spits out a sort of parts list of triangles and other shapes. It's all cut out of vinyl of the the "floor pattern" you've chosen and "seamed" together. It's actually more like a triple stitched weld since the vinyl actually melts a bit. It's done with low intensity lasers.

As far as the main drain goes. If (and that's a big if), it can be repaired, theoretically hammering it out to the point where you can attach a pipe to it and extend it through the added sand is not an impossibility. I've done a few like that, but it was during builds in which the original dig was too far into a water table and the pool had to be "shortened". Also this entire process would have to be done before the liner is measured by any outside parties. Allowing for the variations in how it might be done would be far too complicated.

The liner can't really stop at the deep end or terminate anywhere underneath the water for that matter. Unless something has been specifically designed to receive it that way. At one point in history a pool was created opposite of how you describe. With a liner in the deep and shallow ends but terminating about 6" up the wall. The wall was designed with a water proof "track" to receive a normal liner in it. The theory being that most liners fail above the waterline due to UV and chemicals accumulating on the surface of the water. I believe the company was named Polynesian or something to that effect. They were a miserable failure and plagued with problems. It was a short lived design. I've only seen two, one is still hanging in there, as I said plagued with problems. The other was torn out completely and the hole was reused for a new pool.

Liners were intended to "line" the pool's entire volume of water, that's how they work best, IMO anyway .

A liner can be measured to fit the "shelf" and your steps, and just about anything. How well, and with how few or no wrinkles is the question. A liner company might guarantee the fit if they themselves measure it, but it costs to have a team of them come onto the site and do that. They might not even guarantee it if the pool is far too irregular.

Tapconning or whatever method you use to attach the extrusion (track), is another story. With a rigid metal track there's more strength to it, and they require less fasteners. With something more durable with the water a plastic for example, they need them every 6". The track is usually the same as any other one for a vinyl liner. But it's only the slot itself and no coping or decorative edging to finish it off, or receive a concrete deck. It's basically a rail with the extrusion as part of it. Except it's mounted vertically (the slot) and the liner goes up and over the forward edge of the rail, and then down and into the "slot" itself. The few I've done were "spec'd" out this way by the vinyl people. I think it allows for the rail itself to be more narrow as it now would not have to accommodate the size of the liner bead horizontally. A wider or thicker rail with the liner bead inserted horizontally would have a lot of down force or pull on it. In close and tight to the wall or "thin" is better when exterting downward forces.

Whether the pool is gunite or concrete makes a difference too. Gunite is not really all that substantial of an material to drill into. Since it has no aggregate (stone in the case of concrete), it's more like mortar or grout when drilling into it. Gunite tends to deteriorate from drilling and holds fasterns not nearly as well as concrete. Plus if it's gunite there's a layer of plaster that dulls drill heads quickly since most pool plaster contains a an element of marble dust as part of its make up.

I've not done a lot of gunite or concrete work and sealing anything like cracks in either of these materials is a whole nother discipline. The times I have done it, a "V" groove is carved out of the crack itself to widen it. Then a water proofing like mortar is added. Thorite or some kind of water plug. Caulking below the water is rarely used since it always remains "gummy" after water is added. I suppose a two part deck sealing epoxy might do the job, but I don't know about it be submersed for long periods. And if the cracks are on anything other then a flat surface deck sealing products don't work well, they are very "runny". Unless your referring to cracks in the deck, then disregard this last part .

If any of this doesn't' make sense.......I'm not surprised. Something always gets lost in the translation when things get this complicated.