According to Joe at White Oak Audio Design,
https://www.whiteoakaudio.com/estore.aspx
It used to be a good idea to match the hFE, or Forward Current Gain, of the output transistors to make the amplifier more efficient.
Today, with modern robotic construction, better design, and higher quality materials, the consistency of modern, new power transistors makes gain matching unnecessary.
When I order 100 MJ21169G Output Transistors, they all have the same date code. I spot check the Gain of maybe (10). They are all within one or two units of Gain measurement on my Sencore TF151A Transistor Tester.