Occam's Razor: The Leaking Toilet

Occam's Razor says that given a problem with several solutions the one with the least number of variables is probably the best. I can now apply this problem to the leaking toilet in our apartment.
When we installed new flooring in the bath and kitchen we ended up with a toilet that leaked. At first we thought it was because the floor had been raised above the toilet flange but after several modifications that didn't seem to be the problem. No matter what we tried there was water on the floor next to the toilet in the morning but only after Alan and Lindsey had showered.
Last Saturday I returned to the scene of the crime to try and fix the leak again. We suspected that there may have been some backing up from the drain line as the toilet only seemed to leak in the morning after the tenants took a shower.
So I pulled the toilet and filled the tub with water and let it drain while pouring water into the toilet drain. There was  no backing up of water so the drain line was clear.
When I pulled the toilet it was obvious that the wax ring had failed and the new extender flange I had attached was also warped. I decided to remove everything and installed a different kind of extender. I sealed the attachment to the base with silicon sealant and put everything back together. I also used stainless steel washers to attach the toilet instead of the aluminum ones supplied. Once more I filled the tub with water and pulled the drain while flushing the toilet. There were no leaks. I waited an hour and repeated the process and there were no leaks again. I was sure I had fixed the problem.

no leaks around the floor seal

Later in the week I talked to Alan and he said that there was still water next to the toilet in the morning. I asked if there was any water before they showered and he said no, only after they were done with their showers.

Water puddle outlined in black

So I called my brother Delwyn (every family needs a plumber and a computer guy) for advise. We explored the possibility that the drain vent was clogged and then Delwyn suggested the obvious, the shower was leaking. Rather, as Alan and Lindsey used the shower water was getting around the curtain and running to the low point in the floor to the right of the toilet.
We devised a test. We had them put a towel on the floor between the toilet and shower before they went to bed. In the morning after their showers they checked the towel and it was wet and there was no water on the floor to the right of the toilet. Problem solved.
I wonder now if the shower was leaking all along and that we never needed to pull the toilet. A good lesson. We'll put a corner piece in the tub to redirect water and ask them to close the shower curtain better. Hopefully I can check this off my list of repairs needing to be done.