The first BY bm Nr is 1123, but last UA bm Nr is 1083! Once, in the days of the USSR, it had nr 1122, but after regaining its independence by the UA numbering of the bms collated. The numbering of the PL-USSR bms was ordered until 1951. From 1 to 2439. In 1951 between these countries were the exchange of parts of the territories: http://en.wikipedia.org/wiki/1951_Polish–Soviet_territorial_exchange . After the change the border ran: from tp marker „Krzemieniec” (between the borders of Poland, the USSR and Czechoslovakia) to the marker 224 (source of the River San), further by San to marker 350, from marker 351-A to marker 432-A (section land border set in 1951 as a result of the exchange of territories), from marker 472 to marker 700, from marker 701-B to marker 859-B (section of the border set in 1951 as a result of the exchange of territories), from marker 860 to marker 1437 (boundary runs the River Bug), from marker 1437 to marker 1987, i.e. to the present LTPLRU tp  and from 1987 to marker 2439 where it ends (section of the border in the former East Prussia). After bm Nr 432-A was bm Nr 472 and after bm Nr 859-B was 860.

 As you see: 472-432=40 (this gives the 39 sections between the bms.). It is interesting, that on the present PL-UA border there are two nr 351 border markers!   Old 351 and new 351 (ex 351-A).