Thanks for raising this as an issue. The [TB] block specifically targets the US portion of the copyright tags, so it is worth teasing this issue out a little.
I assume both of you know about: http://imslp.org/wiki/Public_domain#Russia_.2F_USSR
and: http://imslp.org/wiki/Public_domain#U.S ... 3_and_1978
I would surmise from the former paragraph that Medtner, having died in 1951, should have been in the public domain in the USSR at the time the US copyright restoration went into effect. The complete works edition from Muzgiz is probably completely PD, although I wouldn't rule out there being some exceptions from his œuvre: there could conceivably be editorial completions of incomplete works, or lyricists/translators of any vocal works who lived beyond the cut-off date c.1953; also note the general editor Goedicke lived to 1957, so any copyright pertaining to his editorial contributions would have lapsed only in respect of Canada. Thus the Muzgiz score of the Op.59 Elegies probably ought to have the same copyright tag as the remainder of the Muzgiz complete works edition.
The Zimmerman score of the Elegies published in [the former West] Germany in 1953 is
correctly marked with a US copyright expiration of 2049, so my assumption is that the copyright tagger of the Muzgiz score applied the same tag, assuming the same copyright issue to have held: probably just a simple mistake, rather than malicious inconsistency.
If there are any other of the Muzgiz scores tagged incorrectly, please PM me and I'll check them. I am not as au fait
with the intricacies of US copyright as certain others of the Copyright Review team, so I'm only marking these US tags as "checked", rather than "verified"; however, that is sufficient to remove the TB block and allow the scores to be downloaded.