I will paint with a very broad brush and say that postage stamps and revenue stamps are used/canceled differently. This may take two different angles of thinking. Postage stamps are typically canceled by the PO with fairly standard handstamp and machine canceling devices, creating a certain uniformity. Revenue stamps are very often canceled by the individual user (like you or me) or small businesses and thus often will have a variety of manuscript markings of initials and dates, or handstamp markings of the business involved, not necessarily intended to cancel revenue stamps. Here are two promissory notes showing such. Your 50 cent stamp is of similar use, soaked from a document, very typical.
It is not possible to interpret your other written-on stamps without images.