I suspect that this has been answered before, but I cannot find it.
It seems like it is possible to abuse the retreat rules to move units more spaces than they should be able to.
For example, (R1, original placement) Russia attacks Germany held W Russia from both Caucasus and Karelia.
After just one round, all of the attacking units in Caucasus can “retreat” to Karelia–which would be a a two turn move for infantry and artillery from Caucasus to Karelia, if W Russia were instead already held by Russia.
I’m sure I’m not the first person to have thought of that, the wisdom of that particular move being besides the point. Is that considered a legit move, or can you only retreat if eg you have some movement allowance left?