Interesting. It has always appeared an oddity to me, coming out with such a fabulous Top 5 single and then hearing nothing much more for such a long time, and then smashing to No1. A strange choice not to nurture such clear talent, who had numerous top 5 80's classics in the end, none dated to this day.
I think I'm right in saying that 'Use It Up, Wear It Out' climbed the chart and got to number 1 around the time of the 1980 Musicians' Union strike that took TOTP off air for at least a couple of months. The singles chart without TOTP's influence was an echo what happened in 1974 - black music flourished and, in that climate, Odyssey scored their first number one. Would that single have become as big a hit with no MU strike and TOTP intact? We'll never know ...
I would also hazard a guess that, by 1980, it must have become clear to RCA in the UK that some of the artists they had been spending time and money promoting (e.g. Bonnie Tyler, Gerard Kenny) were either no longer generating hits or indeed never going to, and so it might be worth putting a bit of welly behind a group that could land a number one without any TOTP exposure. And so began Odyssey's three-year run of hit singles ... all after disco was declared dead in the US!