TL;DR Talking about hypothetical guarantees, French guarantee is valid, not sure about Yugoslavia. Also Czechoslovakia could have a guarantee from Soviet Union as well (really), at least very early in game.
Czechoslovakia was one of the first nations to recognize Soviet Union and tried to maintain somewhat friendly relations, mostly to try to keep away fascist Germany, and revisionist Hungary, since French Influence in the region has been dropping for a while now.
But we 'failed' miserably, because in order to put some more diplomatic weight behind the alliance (as a small country) with USSR, we put an article in the treaty stating something along the lines 'but only if France agrees to go to war with Germany first'. And when Munich came, french abandoned us, and since USSR did not want to potentially face German agression alone, to save a single small country (also how would they cross Poland?), without France, they used this as an excuse to consider the treaty invalidated. RIP Czechoslovakia.
Czechoslovakia was one of the first nations to recognize Soviet Union and tried to maintain somewhat friendly relations, mostly to try to keep away fascist Germany, and revisionist Hungary, since French Influence in the region has been dropping for a while now.
But we 'failed' miserably, because in order to put some more diplomatic weight behind the alliance (as a small country) with USSR, we put an article in the treaty stating something along the lines 'but only if France agrees to go to war with Germany first'. And when Munich came, french abandoned us, and since USSR did not want to potentially face German agression alone, to save a single small country (also how would they cross Poland?), without France, they used this as an excuse to consider the treaty invalidated. RIP Czechoslovakia.