The bottle of TMAX RS I have is from a camera shop that had closed, so I got a good price.

I had resolved to not add the packet, but if something definitive turns up before I start my testing, I will use it. I will continue to search as well.
From what I've read, the concentrate is quite long-lasting - I just need to know if the same is true of RS after the packet is added. Mixing as needed sounds like a good route for me to take, considering my low-volume of B&W film.

I'm slowly acquiring film and chemicals to try some things out in 35mm, so I've got some time. A recent Bronica acquisition has slowed me down a bit .