On a tangent...
The majority of mail is posted with the most common stamps, thus if there is any monetary value, it may be in the other "postal history" aspects. This includes the sender, recipient, postmark, evidence of handling/mishandling, etc., etc. The postcards themselves can have value too. For family items, the value is often only sentimental. And lastly, the Antiques Roadshow mantra applies that "everything is condition, condition, condition"
For the cancels, the attractive "flag" cancel on the first card was used in Lyndonville from 1911-1931, thus very common and retails in the $1 range.
The second card also has an interesting cancel similar to the one below). In 1920 Boston numbered their stations and nearby suburbs with a "Zone Number" to help in sorting mail. Roxbury was assigned #19. This is one of the earliest forerunners of the modern Zip Codes in the US with 021
19 still being in the Roxbury area. Retail is a dollar or two for mailpieces in nice condition.
