A sparsely catalogued part of modern Latvian philately are provisional stationery. Soviet postal stationery uprated with a rubber stamp with the text: "
Pasts Latvija" (Post Latvia; read from the left) and a face value in kopecks.
The latest Michel stationery catalogue on this topic - the
Michel Ganzsachen Europa ab 1960, Westliches Europa 2011 has some of these listed (U 7 to U 17 with U 18 to U 20 reserved; page 382), but there are many more not listed, even those that would be considered as regular issues with only one rubber stamp.
To make a long story short ... at the time in question Latvia had 27 administrative regions. Each of these regions had a postal management and those regional postal managements were made responsible for the sale and distribution of provisional stationery. The story does not tell who actually applied the original rubber stamps, but it does not require much imagination for a dubious character of a postal employee to come to the conclusion, that such a rubber stamp is easy to copy. And that is how we end up with the following postally used covers.
The regional postal administration of Preili, in the south-eastern part of Latvia, did something unique. They had a rubber stamp made with the face value "50", which none of the other regional postal administrations are known to have used.
From December 1, 1991 to February 29, 1992 the rate for a domestic letter of the 1st weight class (<=20g) was 50 kopeck.
From March 1, 1992 to August 9, 1992 the rate for a domestic letter of the 1st weight class (<=20g) was 1 rubel (100 kopeck).
Soviet postal stationery with 5 kopeck imprinted postage stamp, uprated with a 45 kopeck provisonal rubber stamp to get the 50 kopeck rate. Then additionally uprated with the Preili 50 kopeck provisional rubber stamp to get the 1 ruble (100 kopeck) rate. Postmarked in Riebini (hard to read) on July 20, 1992. The cover was sent to a postorder book store in Riga, and the paper remnants in the upper left corner are from the order slip that was glued to the cover as reference.

Same story with this cover, even though the Preili 50 kopeck provisional rubber stamp was first applied to a sheet of paper, then cut out as a regular postage stamp and finally affixed to uprate the cover. How about that? Postmarked by machine cancel in Preili on May 7, 1992. The cover was sent to the Ministry of Social Welfare in Riga.

Backside of cover with postmark of arrival.
