Remember "the bigger the office the worse the care"
As to recurrent caries if you removed very old ones in the range of thirty years then yes under some of them you will find caries but not all of them and not at 5 years. I have removed many thousands over 25 years.
That said, I just had a very large filling removed to be replaced, that was only done in 2011, originally done in 2008 - and apparently there was some decay under it and a piece of the tooth fell off as the dentist was sorting it (about to have inlay fitted this evening).
I haven't had an x ray in over a year but wonder if it would have shown, if I had? I had no pain, just really minor discomfort that was fleeting, and rare -and only casually mentioned this at all, as I had a new dentist and she asked me if anything was bothering me, during a routine check up.
This scared me considerably - as this filling had already been re-done, in 2011 so was fairly 'recent' and as I say, only neglible twinges now and then. I had a sedative filling on it for over a month and when that came off to do the impression for the inlay, dentist said my nerve which ahd been inflamed, seemed 'recovered'.
So whilst decay under an amalgam filling is a rare thing - it can happen and with no warning. I was pretty horrified when she said she wanted to re-do the filling, and moreso when she found there was decay (and risk of RCT because of that) under it.
I'm left wondering how that could even happen? From what you say, comfortdentist, what happened to me is a very rare thing? (trust it to happen to a phobic)

) Was I just unlucky or should this have been detected sooner? (Dentist did file it down a bit in 2011, as I just thought my bite was out).