Well, under the 'exceptions to regional regulations' on page 24 of the synopsis, under the Chilliwack/Vedder Rivers specification, it reads...
No Fishing upstream of and including Slesse Creek- No prob, that's clear, I know where that is.
Downstream of Slesse Creek to Vedder Crossing Bridge, under the b) hatchery rainbow trout of any length 50cm or less: daily quota = 4, July 1- Apr 30
Downstream or Vedder Crossing, under the c) hatchery rainbow trout of any length 50 cm or less: daily quota = 4, July 1-Apr 30
Hatchery Steelhead daily quota 1
That's where I got the 4 RH 1 sh. Since they seem to consider under 50 Rob and over 50 sh, they are mentioned as different fish.
Not that I expect to actually come even close to those numbers...