Before Oyster, London used to sell books of bus tickets. Other operators could have implemented something similar if they had implemented flat fares. Given that many towns now have flat fares within urban areas, it sounds hard to believe that they couldn't have done that 20 years ago.
Multi-journey tickets exist outside London and have done for many years. When I was at Western National in the early 1990s we had 9 journey tickets, issued and cancelled (so there was a more detailed record than "Pass" in the system) on Timtronic machines. Issued on a square card, the first journey was printed in the centre and validated the card, subsequent journeys were printed around the edges, two per side, and no end of trouble ensued if the driver incorrectly selected left or right and the machine over printed a box! Timtronic used fares look-up so there was no need for flat fares, and when programming the fares it could be set with different zones so, as an example, in one area you might sell 9 journeys for the price of 8, but in another for the price of 7, dependant on the availability of other tickets for that journey and what you wanted to promote. Set a fare-stage specially for a school or college and you could give them a special rate, if you wanted. Slow? Yes, fairly, especially on a busy peak hour buses where such tickets were popular, but it worked, and lots of people used them.
In the latter 1990s I used multi-journey tickets via Wayfarer 3 magnetic cards, which could be unreliable, but were well used.
And in the area I now work local authority supported services offer multi-journey tickets, originally with the paper ticket inserted into a wallet with journey numbers along the edge which would be punched to cancel them. The same approach was adopted by the major independent in the area for their commercial, and originally competitive, services. Now Ticketer prints the number strip.
None of the above are Oyster, but then, none cost anywhere near what Oyster did to implement.