I believe I've seen 1958 several times.

There are many, many variations of the 26C/F control valve. Besides the generational changes, the charging chokes and additional charging checks can be varied. I've heard Amtrak uses two different "standard" versions, different from the common one used on present locomotives. There were versions that were designed for charging a larger auxiliary reservoir, and the brake cylinder volume was small enough it didn't use a relay valve and supply reservoir. The San Pedro Trolley has its own unique version to provide for a rapid recharge of everything to be able to make the next stop.

I did find a parts list years ago (can't set my hands on the copy easy) that was a "26" (no suffix) engineer's automatic brake valve. It was the obvious predecessor to the later 26B/C versions. A friend found a very early 26 control valve that had a release built into the cover for the main diaphragm. All information points that it was a transit valve that was applied to several transit/passenger projects, before being adapted/adopted by the freight side.