Exactly right.
When we had the asset system, riders were given a percentage of the transfer fee. I think 2.5% of the fee for each year they had been attached to the club. (Although it may have been 5% for the first year and then 2.5% for subsequent years up to a maximum of 25% or 27.5% - someone will remember).
Testimonials were compensation for a rider who had stayed an asset of a club for 10 years, and had therefore never had a cut of any transfer fee.
It was also possible to be transferred to another club, but refuse a cut of the transfer fee, in which case the years of service continued to build up towards a testimonial.
With the asset system seeming to have bitten the dust now, I guess Testimonials will also disappear.
Someone will know the cut of the transfer fee. I think it was 5% for the first year, and 2.5% for every other year up to 10 years.