I don't speak English to a good degree, about the same as You the Russian language , so there may be difficulties in translation.
1) I don't understand why the Dating of 1870? On the dial inscription "33 clockspur" it 1857-1861 year.
3) unless after 1861 was not the inscription 33&34 clockspur?
The proof I have is this comparison of the details of the movement of Audemars - his own style.
I think you're doing just fine with your English, Edgar

I am trying to keep my English simple for you, but that is not always possible ... so please keep asking me to explain what I am not making clear
You have to realise that dating Dent's just from serial numbers is very difficult. That is because production records of movements are usually not available, so most dating is done from the hallmarks of cases which contain the movements. That method of dating is sometimes unreliable.
You are right that if you only use your serial number to date the movement, according to Vaudrey Mercer's book the estimated date could be about 1861. But in a separate part of Mercer's book there is a list of movements supplied to Dent by outside makers. It is not clear what this list represents, but I believe that the list is taken from book records of the Dent company, and the list shows a group of serial numbers, followed by a maker's name, followed by a year - which must be the year these movements were delivered to Dent by the maker.
This list must be much more reliable than any estimates of date from hallmarks.
Your serial number 26218 is included in the group shown in the following entry on Page 699 of Mercer's book:
26215-26226 Nicole 1870
I think that is conclusive that your movement was delivered to Dent by Nicole in 1870, and I am guessing that the movement must have been made by Nicole in 1869 or 1870.
Mercer's book also contains several observations of hallmarked watches, and these include on Page 682:
26374 dated 1870
26834 dated 1871
and these again suggest a date of 1870- for your watch. I have number 26438 dated 1870.
The address 33 Cockspur Street continued to be used for a long time after number 34 was acquired. I have three dated 1882, 1890 and 1895. The only use I have ever seen of 34 Cockspur Street was in 1910, and I have only ever seen 33 & 34 Cockspur Street once (but I can't remember where!).
I can't comment on the "Audemars style", and also I know nothing of the "Nicole style". But is it possible that Audemars was actually using the Nicole style as defined by the Nicole patent for a chronograph?