If you are concluding that non-ATW's are closed during March, then you have to make the same conclusion for most of September and all of October, November, December, January, and February too.
The trout season ends on Labor Day. Not March 1. The extended season applies only to ATW's and goes till March 1. So for anything except ATW's, the time period we are interested in is not just March. It is Labor Day till the regional opening day. If it isn't an ATW, then the regulation has to be exactly the same on Oct. 15 as it is on March 15, for example.
Now, the PFBC flat out states that it is lawful to fish streams listed as class A and Wilderness trout streams year round. It elaborates and says that from Labor Day till opening day it's on a strict C&R basis only, so strict that even accidently harming a trout could find you in violation of law. So how do you take that? That's up to you, I guess. To me it means they aren't encouraging it but they don't intend to enforce a total fishing ban, either. It says nothing about streams that are not class A nor wilderness. i.e. what about class B, C, and D, assuming they are not ATW's? We are left to assume the regulations there would be the same as class A's and wilderness streams.
Clear as mud. Pretty bad that a message board of avid anglers can't figure out the law. But we have this debate every year, and the consensus has always turned out to be:
If it's ATW --> regular season till Labor Day, extended season till the end of February, no fishing at all in March.
If it's not ATW --> regular season till Labor Day, C&R only the rest of the year.
If it's special regs --> follow special regs.
The limits of ATW's and special regs as found in print here:
http://fishandboat.com/fishpub/summary/troutwaters.html