For the purposes of this exercise, I will only include services which run the full length of Old Durham Road between Gateshead and Wrekenton as I feel that this makes for fairer (and easier) comparison. I also won't include the 727 as OK Travel did not fall under the Northern umbrella at the time.

So, currently, we have the 28, 56, X1 and X25 totalling 15 buses per hour. In June 1989, the following services operated:

56: Newcastle - Springwell Estate(every 10 mins)
187: Gateshead - Sunderland (hourly)
188: Gateshead - Sunderland (hourly)
189: Newcastle - Brady Square (hourly)
721: Newcastle - Chester-le-Street (hourly)
725: Newcastle - East Hedleyhope (hourly)
726: Newcastle - Witton Gilbert (hourly)
X4: Newcastle - Sunderland (hourly)
X5: Newcastle - Hartlepool (hourly)
X94: Newcastle - Hartlepool (hourly)

So 15 buses per hour ran between Gateshead and Wrekenton; the same amount as today.

I also have the same timetable for November 1997 so I might as well chuck this in here for comparison too.

56: (every ten minutes)
187: (hourly)
188: (hourly)
189: (half-hourly)
721: (hourly)
725: (hourly)
726: (hourly)
777: Newcastle - Sunderland (hourly)
X4: (hourly)
X5: (hourly)
X90: Newcastle - Ryhope (hourly)
X94: (hourly)

In total, this makes 18 buses per hour for November 1997.