More seats seemed to be the way the industry was going throughout the 60s, which is why I have confidence in the Super 200's ability to generate sales. The DC8 got ~260 seats in 1967, the B747 could have 400+ from 1969 and the DC10/Tristar could get close to 400 in 1971-72, so 212 in 1966 appears to fit the trend when 172 does not.
OTOH if the extra seats on the Super 200 can't be filled, that will reduce the load factors, which in turn may make the economics of the Super 200 look worse (on paper) than the OTL Super VC.10, which in practice was more profitable than the Boeing 707 because the higher seat-mile costs were more than offset by the higher load-factors.
That's why my preferred solution is to put both versions of the VC.10 in service before Sir Giles Guthrie became chairman of BOAC and proving that while they were less profitable than a 707 in theory, they were more profitable than the Boeing in practice.
Also VC10.net says that HMG appointed him to deal with the airline’s large debt which grown to £80m by the end of financial year 1962/3. In my version of the TL the extra profits the VC.10 generated by entering service earlier would have been reducing that debt for 20 months in the case of the Standard VC.10 and 9 months in the case of the Super VC.10.
In my version of the TL the OTL Super VC.10 enters service in April 1963, but at present, I see no reason why it couldn't be the Super 200. Which, means if the extra seats were filled, it would be earning even more money for BOAC in my TL, than the real one did.
In my TL the VC.10 is put into service 2 years earlier because Vickers doesn't do the Vanguard, because BEA & TCA bought Britannias instead leaving Vickers to concentrate on the VC.10. Would that have produced the result that I want? I don't know and have discussed its feasibility earlier in the thread. However, it would have saved Vickers the loss of £18 million that it made on the Vanguard, which is money that it could use ITTL, to complete development of the VC.10 without having to ask HMG twice (in 1961 & 1963) for launching aid, that in the end, totalled £10.2 million, for what had hitherto been, a private venture.