DJ6 & FRatSTN,
Believe it not STN did have terminal buildings pre 1991, the pre 1991 terminal was on the other side of the runway and the original terminal, before that, had become the staff canteen on the other side of the runway, STN had been a fully functioning airport for some three decades or more before the quoted 1991 opening.
So when did SEN open ... Which terminal opening decides when SEN opened?
P.S.
CAA approved Laker's application on 5 October 1972, granting a ten-year licence. However, it specified Stansted rather than Gatwick as the service's UK departure/arrival point and limited the number of seats that could be sold in winter to 189 per trip, the maximum number of passengers a Boeing 707 could accommodate in a high-density, all-economy configuration. The unexpected change of the UK departure/arrival point for Laker's Skytrain service