The BBC did make a colour VT recording of ESC 68. It was shown on BBC2 the next day (Sunday) for the benefit of the small number of viewers with colour TV. This is the only time the ESC has ever been repeated. However the BBC then wiped the colour VT and kept a B & W film copy.
No I've not seen a full BBC recording of ESC 74 either. It looks like only the first reel has survived. I presume they originally recorded the whole show, but the second reel (with the voting and reprise) has probably been wiped.