Brand A's design is probably the application of basic design principles devised by company "X" thirty years before.
Particularly,with RF circuitry,you can make a perfect copy & still not achieve the same results,whereas the original designer knows the limitations & tradeoffs involved.
There is always the temptation to say " I don't think they need that much shielding.",or " It's a lot cheaper to make that track curve as a right angle".
I have fairly recently experienced this in a UHF Transmitter design,where the test board circuit from a manufacturer's app note was copied without knowing why things were done.
In an RF Amplifier circuit,two of these layouts which were driven in parallel,were placed nice & close to each other on the same PCB,reducing the cooling of the LDMOS devices.
They were fed through a hybrid,& the output combined in the same way.
It was "much cheaper" to use marginal inbalance load resistors at the output,so they did.
Even so,all might have been well,if both amplifiers on the board were tuned for the same frequency range,but no!
They copied the chip capacitor values exactly,& positioned them identically,so with normal variations in the LDMOS characteristics,the response curves were sufficiently different to create enough imbalance to cook the unbalance loads.
On top of this,none of the amplifiers were optimised for the frequency we were using---more inefficiency,more loss,more heat!-----But they were perfect copies!
I won't say where they came from,but I bet you can guess!