They weren't commissioned.
The separate ITV companies made them all and the regions were almost obligated to take whatever the 5 main network companies produced .
Remember , at this time , the main companies , Central , Thames , LWT,Granada, YTV all had their own drama and comedy departments so there was a wealth of talent being used and a pool of brains 5 times larger than the one available now.
Over the years there were several occasions when one regional company thought something was so bad they refused to schedule it at primetime so would move it and usually the other region would do the same in a tit for tat move.
IIRC LWT moved an ATV show so ATV moved The Gentle Touch to post News At Ten in retaliation.
LWT's The Adventures of Don Quick was 9pm Friday but even though it was only 6 episodes some regions moved it to after the News before it finished.
Even until well into the 80's all the regions had their own timetable and at times , even primetime shows were still not fully networked.
And until the mid to late 70's even ITV's biggest hits were rarely networked and sometimes not even shown on the same day let alone the same time.
In 1991 C4 had only been there for 9 years so its procedure for producing nothing and commissioning everything was still relatively new and it was an alien concept for ITV.
However - Carlton took the Thames franchise away and part of their plan was to follow the C4 route.
It didn't take long to show that it wouldn't work as there were not enough independents at the time.
So it grew gradully over the years and eventually the BBC even started doing it aswell
But in 1991 the main 5 ITV regions basically shared primetime out amongst themselves and filled 13 weeks a year each with LWT dominating the weekenRAB
