Bother - beaten to my edit when I had the 'hang on, 6 has disbanded' thought.
The answer is that it is possible that IV will overtake 6, but, don an anorak for a moment and let me explain why this might not happen...
...the problem is that when the AHB did the squadron seniority rankings in the late 1950s (to work out which numberplates went after Sandys slashed the RAF's strength) weightings were applied to cover peacetime service and operational service, and this may have carried over into the 1968 rankings. It had been assumed that the 1968 rankings were most likely done purely on accumulated service, but it seems that 43 Squadron appears lower on the list than it should do if accumulated service were the only metric applied. This could be nothing more than a mathematical error, or it could be a hint of how the 1968/73 order of seniority was drawn up. But we don't know.
So 6 losing 3 years between the Jag and Typhoon may push IV and 14 above it, but I suspect possibly not 8.
But - did 6 actually disband?
'Of course it did!' I hear you cry, 'There was a disbandment parade.'
Indeed there was. But... since 6 was already declared as the third Typhoon squadron numberplate at the time of the Jag's retirement, there is a case for saying that 6 didn't disband - whatever anyone who was at the disbandment parade may have thought - but in fact was reduced to number plate only status, since the number plate had already been allocated to a squadron, even though that squadron didn't have any aeroplanes or personnel...
I'll ask the head of the AHB what the actual answer to that is next time I see him, which will delight him, I'm sure.
TD - no it doesn't; the calculation begins with formation as an RFC or RNAS squadron. And you probably realised that you weren't really as bored as you thought until you read the above ....