Anecdote on 2n3773's. I once needed a pair of replacement pro Electron devices ( can't remember exact part but it was a BDYxx series one) so put in an order with stores for 2. A month later I get a call from the head stores, asking how many I would need in the next decade. They were apparently a superseded part, and while the original manufacturer ( now part of the Airbus consortium) still had the masks and the process equipment, they would be a special order. Cost was $100 each, and there was a minimum order quantity of 10k units, with a 11 month lead time from confirmation and payment up front. I was asked if there was a replacement instead for them. So looked in the "transistor bible" and on the page in particular was listed 30 or so equivalents, among stem was the 2N3773 listed as "Improved specs". Checked in stores, and they were both there, in stock ( around 30k on hand) and available for us to order. Placed the order for 4 cases, as they would also replace 2N3055 transistors in any application as well.
When they arrived I used 2 as needed and stuck the rest in stock, looking like they would be a decade or more till finished. Little did I know that next month in would come the first of a line of Tower ferroresonant UPS units, which each either used 50 of them, or a $5k transistor brick. New batteries ( all 4 car batteries), 50 new transistors ( or scrap it if it blew the big silicon block and keep for spares) and run for a week with a 2 bar heater as load after repair. Some got a big chunk of heatsink with the transistors added as replacements. Horrid with the emitter sharing resistors being 10cm lengths of 0.5mm copper wire soldered to 24 emitters, and commoned on an insulated bolt. Transistor 25 was the driver for the darlington thus made.