I think it would not be unfare to say that, in the UK, Reynolds SL was not a very popular tube-set with the many artisan/craftsman builders. For those of them who had been around in the 50s and 60s and who had been able to obtain "531DB" in a very wide variety of gauges/thicknesses (always expressed as gauges eg 22, 24 etc in those days) SL was no big deal, because, according to the Reynolds representative with whom I dealt, it was just the same material re-invented, re-branded and re-marketed. The only perceived differences were the shapes of some of the seat-stays and the different indentations of the chain-stays. The other factor that set it a little apart from 531DB is that the reps. suggested that builders should silver-solder it because of the finer gauges.
I recall a meeting with a salesman for Johnson-Matthey, makers of a range of brazing and silver soldering alloys. He came to visit me shortly after visiting Jack Briggs, at Ellis-Briggs, and reported that Jack had just about ordered him off the premises for suggesting silver-solder for SL, a type of tubes the "Briggs'" had been brazing up for at least twenty-five years. He didn't distinguish whether it was Jack's prowess and skill that had been offended or his pocket due to the relatively high cost of the silver-solder.
On one occasion when I called on Jack in the mid-80s we started reflecting on SL tubes, with Jack bearing out the very same problem that has already been identified on the List - the failure of the chainstays due to the stress-raiser caused by the flat area pressed into inside face of the stay. Jack claimed that he had had more failures with SL frames, due to this one particular weakness that with all the other frames they had ever produced in nearly 45 years.
It was also generally held in the UK among builders that the rear triangle was somewhat inadequate when compared with those produced by other sets such as Columbus and Vitus. Even the Pro tubeset suffered from that same problem. More often I would spec a Columbus SL rear triangle on a Reynolds frameset, as it would give a better feel and greater compliance. Pro bi-conical seat stays were a definite No-No on touring and cyclo-cross frames with brazed on brake studs!
Norris Lockley , Settle...in a VERY wet UK