Note; this might be getting too concerned with detail for the person who asked the original question. Feel free to skim or ignore this.
Originally Posted by Simon Rodgers:
“What I'm saying is, if you get an NTSC compatible player in the UK, the output will be the same as a PAL tape in the respect that UK [television] sets will be able to display it, etc. Like a black box type exercise.”
Yes, but you're missing the point... we're *not* talking about displaying the signal on a TV.
The output from the VCRs in question is likely to be "PAL 60"- a hybrid with NTSC's 525 line / 60 Hz resolution, but PAL-spec colour (and sound?) subcarriers.
It's neither fish (genuine NTSC) nor fowl (PAL), and while it should (*) in theory display on UK TVs that can handle the nonstandard line/frame rate, it can't be taken as given that it'll work with all digitisers and cards, which will process the information differently and have to know what they're working with.
Originally Posted by Simon Rodgers:
“You start with an NTSC tape and a viewable film at the end. What happens in-between, is not really important.”
It's only "not really important" in cases where you're pretty sure it's *definitely* going to work.
Originally Posted by Simon Rodgers:
“Take THAT output and run it through a TV card and record off that. Then the computer will [digitise it].”
The problem is that the card has to know what it's dealing with and able to demodulate it and determine the line structure before it can digitise it. And the (potential) problem is that it might not recognise and/or handle a signal with the resolution and framerate of NTSC, but sound and colour carriers of PAL.
(*) I do know that my parents' (now defunct) early-80s TV didn't like NTSC framerate input... but that *was* rather an old example.
tl;dr version - PAL 60 is a hybrid (NTSC framerate and line count with PAL colour (and sound?)), and while this nonstandard signal might work with modern TVs, digitisation cards aren't TVs, and it can't be definitely assumed they'll work with it. Probably have to check and/or experiment...