25 years of the coronation of Queen Elisabeth, stamp exhibition PHILASERDICA - Block 77 on real run

A very rare real used registered first day cover of the Bolivia stamp block issue No. 77. Canceled with day cancellation from the first day - two box-shaped first day special cancellations for the anniversary “25 years coronation of Queen Elizabeth II” as well as a purple additional cancellation from La Paz in the lower right corner .
On the back of this first day cover is the additional franking in the form of a horizontal strip of three of the stamp issue, issued for the international stamp exhibition "EXFIVIA 75" (catalog no. 903), also with the day postmark dated June 1, 1978, the first day of the block issue . Only 30 to 40 copies of these registered first day covers that have actually been sent should exist worldwide - very rare!