Looks like you have an interesting collection of stamps! Stamps from the reign of Leopold III of Belgium, such as the one with a lion on it from 1936, are certainly historical pieces. Leopold III reigned from 1934 to 1951, so stamps from that era are valuable not only from the point of view of stamp collectors, but also for history buffs.

And as for the 1938 Conference Aeropostale stamps, one of which is a misprint, that adds even more uniqueness to your collection. Misprints are often highly sought after among collectors due to their rarity and the interesting story behind them. Have you had these stamps appraised yet? It can be helpful to know the value of your collection, especially if you're considering selling or insuring it.