Cause of Sudden Leak in Toilet Supply Line

[SBa]

I have zero plumbing experience, so I'm hoping someone here can help me out. The basic question is this: Is it possible that a supply line valve that was not fully tightened at the time of installation can cause a sudden and significant leak six months after installation? This is a toilet that was barely used until a few days before the leak began. More details below. Any information would be greatly appreciated, as I have two different plumbers telling me two different things and one of them has a vested interest. Thanks in advance!

Additional details if you need them: I had new toilets installed in my home. Six months later when I was out of town, I received a call about a significant water leak from one of the upstairs toilets. The plumber who responded (who is not the plumber who installed the toilet) said that the supply line valve was not fully tightened. The bathroom was seldom used (it was a guest bathroom that was only really used for the first time for a couple days immediately preceding the leak — the house was vacant immediately following the last use of the toilet and for roughly 36 hours before the leak was discovered). The plumber indicated that even though six months had passed since the installation, given the usage, he believed that valve hadn't been fully tightened at the time of installation. The only thing he did to fix the problem was tighten the valve. I notified the company that installed the toilets and they're adamant that it's not possible — that if the valve hadn't been fully tightened at the time of installation, the leak would have occurred immediately. Are they right? Has anyone encountered this type of scenario? I'm not looking for a specific opinion on my leak, so much as I'm just wondering what is and what isn't theoretically possible.

Again, thank you for your time and your thoughts!

 

[WorthFlorida]

The valve may have been hand tighten only (not finger tight) but enough to block water from traveling around the threads. At any time for whatever reason the water pressure increased enough, either from the city water supply or a water hammer event, that it worked itself around the threads and removed any debris that may have been holding it back for six months. Even vibration from water running in the pipes can slowly loosen a bad thread. This type of leak could have been a drop or two an hour or a day for weeks and not noticed until the leak grew larger. It's a hard call but at least the problem was corrected before major damage occurred.