You can also do a pretty fair job of dating it another way, ie. there's more than 1 way to skin a cat.
The London Small Arms Company Ltd operated as a manufacturer between 1866-1935, (but no catalogues exist, or at least have been found).
So we know it was made between 1866 and 1935.
James Paris Lee and John James Speed both have patents; the last of them pertaining to this rifle, date from 1887. So add 17 to that number & we have 1887 to 1904 as patents only had to be acknowledged during their 17 year life span.
The London Proof Marks are the 1887-1904 pattern.
Lee pattern rifles were started to be manufactured for sale in 1888.
The Deeley patent bolt head (patent #19,145 of 1890 further tightens up the date, at least on the early end, because British patents expire after 17 years.
So, we now know we have a rifle manufactured & proofed between 1890 & 1904.
I don't see an E on the barrel knox form, but as has been noted, you could specify a Metford rifled barrel with your order right up until the beginning of the Great War. You could also still order a brand spanking new Lee Metford II* pattern rifle from B.S.A.Co. & one would presume, absent evidence to the contrary, also from L.S.A.Co.Ld., their main competitor for the commercial market, right up until 1914, although we have evidence, via the proof marks, that the rifle was produced prior to 1904. If it had been re-barrelled, even before 1904, it would have been re-proofed & so marked.
Your best bet is to remove the forearm & take some photos of all of the markings on the barrel below thew fore-end.
As Smellie roughly stated "Usually, but not always, people purchasing government pattern arms wanted & ordered the then-current pattern." But as we can see from surviving B.S.A.Co. catalogues, that was not always the case. Of course, the same could be said for the Martini, as W.J.Jeffery, among others, were still offering commercial pattern Martini rifles in .577/450 until just before the Great War.
Of course he also stated:"It's been 100 years since first delivery and there is STILL nothing that can beat a 1910 Ross!" a statement with which I bet a heck of a lot of Canadian troops agreed with; Not a boot, not an entrenching tool, NOTHING can beat a Ross (open). R.I.P. Uncle Cecil. 1st CMR