3.6.15 re-released with a fix now based on regular expression. I've tested in in various ways and it seems to work now.
Looks good. I can still break it if I try, by doing weird stuff like:
19970303T12 becomes 19970303T12T000000.
19970303T123456T000000T123456 becomes 19970303T123456T123456.
...but that's me trying to trick it on purpose. For regular use it looks to work fine: the multiple T000000's that got in there automatically, are now automatically removed, date codes with proper 6-digit time stamps are preserved, and ones without are given a single T000000 (which is then preserved.)