I do enjoy watching fosw and it's a shame there was not more, I think Alan Bell in his book thought it would take over from LOSW as they expected losw to finish after extra extra, the gaff with the trio not knowing Seymour was a major oversight with Roy Clarke as he wrote fosw after the introduction of Seymour in losw, Alan Bell told me if he had any dealing with fosw that would of been picked up as the chap that run the losw appreciation society used to get the scripts from Roy and check through for errors before filming started
Now that's very interesting.
So Roy Clarke effectively had a script editor to find any continuity errors from earlier episodes?
Continuity over 31 series of LOTSW is generally very good, considering there are about 295 episodes. It would be hard for Roy to remember everything on his own.
That would explain why the Seymour problem exists, as a different department produced FOTSW.
There have been continuity errors and duplicated plots that have gone unnoticed, examples include Wally Batty having a different name in the pilot, Compo's school friend's name changing from things like Cloggy, Clogger, Coggy (don't quote me here), and the hearse sequences in Barry's Christmas and another episode (it may be A Leg Up for Christmas, don't quote me here).
A good idea to have a fan to check all the detail, often the fan knows more than the writer when comes to trivial things.