This is an interesting area that needs some further study: the label shown certainly appears to be a *later* version of the 'red seal' design. I think you'll find that the label (a) is fairly small -- about 62mm (as on the 7-inch black G&T discs) -- and (b) has a small rim around the edge (I think I can just see that in the picture). The disc will also show a stamper number (perhaps III ?) next to the catalogue number in the black area.
The same small 'red seal' design also appears on 54757 (Primo Vitti, Roma, April 1902), with similar (sans-serif) lettering around the edge. Here, though, the label is on a standard raised centre area instead.
The earlier design of 'red seal' labels for 7-inch discs was very much bigger (around 78mm) and completely *flush* with the record surface, and with larger (serif) lettering. Pressings I have seen all have a stamper number II.
I have not seen any 7-inch red-label discs without the 'angel' back -- which in itself means a pressing of at least April 1902, when that was introduced. So it might be that the red labels were indeed added at that time. Earlier pressings of these discs that I have seen are in Berliner form, without angel back and also with no stamper number (II or III).
The 7-inch 'ordinary' Berliner pressings lasted until perhaps August 1902, so the *black* labels didn't appear on them until quite late. 10-inch discs, however were getting labels by late 1901.
Lastly, the earlier Berliner versions of these 'red seal' discs that I have seen show 'Reproduced in Hanover' on the back, and the red-label versions show 'Reproduced in Russia' -- so that may help to date the change, too. I would guess that the red labels were added to these 7-inch Berliners (of Figner and Vyaltseva) indeed around May 1902 or so, depending on when the Russian pressing plant was started.
A later comment: I've now checked through a number of Russian 7-inch discs, and can find only one that has an angel back *and* 'Reproduced in Hanover'. All my other Russian 7-inch discs with an angel back say 'Reproduced in Russia'. The exception is one of the very first (temporary) angel designs from April 1902 that have the word GRAMMOPHON (instead of GRAMOPHONE) displayed twice around the angel design. (The factory at Hanover were told to correct that immediately by the London office, apparently; so there are not so many discs at all with that version of the angel back.)
On the other hand, one of my very few 10-inch Russian discs has an angel back *and* 'Reproduced in Hanover', so we need some more data from the 10-inch size, I think. And to put the cat amongst the pigeons (as we say), I'm sorry to say that this 10-inch disc (22551, Morskoi) is without paper label -- it's a Berliner...
I doubt that the "Red Seal" label on 7" records was issued long before November 1902, when Emile Berliners European main patent of 1887 expired, and the then obsolete patent stamp ("E. Berliner's Gramophone, Covered by English and Continental Patents") demanded a redesign.
You have cited Mr. Petts remark that "The 7-inch Red Label discs were issued in May 1902" but I haven't seen any evidence for his claim. Did you?
Dating the "improved" brake mechanism is difficult, as it doesn't seem to be patented and advertisements by the Gramophone Co., Ltd. haven't been placed before December 1899.
But I found a remark by Peter Martland (Since Records Began, EMI, The first 100 years, London 1997, p. 43), that the Berlin office - mentioned on the sleeve - was established by Theodore Birnbaum only in November 1899 and I expect a synchronous opening for N. M. Rodkinson's St. Petersburg office.
I therefore second a printing date of late 1899 at the earliest. Most likely for the Christmas trade.
On the whole, we don't have very early printed record covers like this in the UK, but instead we often find plain coloured thick paper without any printing. The early paper covers that turn up here usually seem to be from continental Europe. I think that Berliners may have been sold in the UK without any covers at all, and customers just bought standard plain covers for them. (I have some Berliner discs with a dealer's label attached to the actual disc surface.) So it is good to see some paper material as old as this.
The gramophone in the picture is like my own and may be from 1900 -- it's *not* the same as in the (1899) HMV trademark picture, as the brake mechanism here is a small 'bolt' on the top instead of the original lever at the front (at the right-hand side in this picture).
I presume that this cover is earlier than the incorporation of The Gramophone & Typewriter Ltd (late 1900), so it may therefore be from some time between late 1899 and late 1900.
If I can find out more about the company's usage of 'Ltd' or about Mailund, I shall post another comment. The printer's mark I shall leave to you! -- maybe a directory of businesses or telephones in Riga around 1900 will give you the full name, as the first few letters appear to be quite readable.
[My first posting on this seems to have disappeared -- luckily!]