At least one of the older tube amps was released with minor variations of the circuit. For mine, the MC40, the older version of the circuit is the one seen in virtually every schematic found online. I only know about the newer circuit because it's in the printed manual that I have; it has dotted lines and notes referencing the older one.
The reason it's helpful to know about the newer circuit is that it has fewer components - two fewer capacitors on the main circuit board, and more significantly, one fewer resistor and one fewer capacitor in the power supply. This last item means that it's more feasible to replace the expensive, bulky, and difficult to source multi-section FP-mount can capacitor with a single-section cap (with high enough voltage rating). The power supply just ends up having 4 caps: the two in the voltage doubler, a big one for B+, and one much smaller (so an axial lead part can be used). I am mod'ing my older one to use the newer circuit while I rebuild the pair.
Presumably the newer circuit is at least marginally superior as well - I doubt the changes were made just to save a few cents on parts (the newer version is still manufactured with the multi-section can).
The attached snippet from the schematic shows the relevant section; bear in mind that the values of two resistors on the circuit board (R11 and R12) are also different between the two versions (as well as some capacitors not related to the PS).
NOTE: I just edited to show the complete newer version of the schematic.