Indoor wall construction - Bolt and anchor

This question should have been easy to answer online but I'm not getting any specifics in the material I've found.  So, I'm hoping the community can help.

When lead climbing indoors, what is a standard construction for anchoring the lead bolts to the wall?  Do bolts go through the plywood and into the structural support in the back?  A stud or steel I-beam?  Or, is it sufficient to meet safety factors to anchor through just the plywood with a t-nut?

I'm trying to find a local gym that I can practice at, however, several climbers in the area have expressed concerns about local construction standards - saying the bolts are anchored only to the plywood and not the structural support as well. So, I'm trying to see what the standard is to understand what to look for and what kind of risks I might be exposed to.  Two years living here and I don't climb indoors much, but I want to train more so I figured I should try to settle this concern one way or the other.

I visited a local gym recently that has quite a few lead routes to see how it was constructed.  The anchors at the top were chains and hangers into a steel I-beam, so that was nice, but the few wall bolts I could see from the back were anchored through the plywood only with a t-nut.

I don't know the size/material of the t-nut, but it looked like this -- https://www.euroholds.com/en/t-nuts/22-screw-on-t-nut-10mm.html 

Any information the community can offer would be greatly appreciated.

In europe it should be 100x100mm square 6mm steel plate drilled through the center and an m10 nut welded to the back. Held in place with woodscrews.

Edit; I wrote that on my phone in a hurry! In Europe there is a standard for artificial climbing structures which is EN 12572 and gives the guidelines for wall construction. The mounting points for protection bolts and belays are specified and from memory they are as above (I actually make the things for a wall manufacturer but I´ve never bothered to get the standard, I make what they specify). You can also go throught the structure and the bolts and backing plates/washers are specified but for intermediate points this is often a poor idea as it restricts setting the routes.
The anchor points are also tested (I make the testing fixtures for another company that certify walls) and the requirement is 8kN test load and 20kN design load in 18mm marine grade plywood. T-nuts are completely unnaceptable.

Thank you, Jim. That gives me a good place to evaluate what I'm seeing over here.

That’s actually a very good topic. I also had trouble finding specific information online. However, I do remember that I read somewhere that in Europe there is a standard for artificial climbing structures which is EN 12572, including all the guidelines for wall construction. I needed that information when I was looking for a new place, but we ended up settling in Singapore and the standards are different here. We ended up finding a place that was completely ready to move in, we just hired some painters from paintingservicesingapore.sg/ to freshen up the façade.  

A pull-test is always fun.