12/13 years ago ERF wasn't widely known at all and was only spoken about in the depths of internet forums. You had to order seats from specialist dealers and it wasn't easy to find them. Most people had no idea that larger rear facing seats even existed. They definitely weren't available in Mothercare and Halfords. There was a verrrry occasional long AIBU thread about it (which would go mostly like this one, just with younger ages and more on the "Huh?! Where do they put their legs?" side) but mostly discussion of ERF was limited to "What car seat should I get?" threads and most people didn't bother writing or looking for a thread for that, they just went to Mothercare and chose from what the salesperson suggested.
It was about 2013 I believe that the first ERF seat hit high street stores - that was the Cybex Sirona, the original had an impact shield for forward facing and 5 point harness for rear facing, and it was very expensive at the time, about £300 IIRC? Maybe even over that. Bearing in mind, a reasonable price for a seat back then was about £60-120, and the expensive ones (like Maxi Cosi Axiss, which was FF only but the first "spin" seat, turned to the side) were about £150. 2013 was also the launch of the new i-size regulation, which also started a wider conversation about the safety benefits of ERF since one of the rules was RF up to a minimum of 15 months.
MN RAVED about the Axiss BTW - it was all anyone wanted from about 2010-2013 or so. Isofix was also marketed very heavily as this big new safety innovation if you had it in your car, which a lot of people didn't, so the fact that a lot of the ERF seats (if you had even heard of them, which most people hadn't) were belt fitted really put a lot of safety-conscious people off. There were isofix ERF seats, like the Klippan KISS, and the Axkid Kidzofix, but those weren't well known and again, they were expensive. That's why the Sirona, and the Britax Dualfix, which followed shortly after, were revolutionary.
I am fairly certain John Lewis never stocked the Two Way Elite but they almost definitely would have had the Britax First Class, which was a two-way seat but only 13kg RF, then 18kg FF.
Joie had released some seats in 2013 but I think they were only really sold through Toys R Us initially. So ERF started to become more well known because of the sudden availability of these spin, ERF, isofix seats sold in major high street chains. But still they were totally premium seats, most people didn't touch them because they were too expensive or because Maxi Cosi were by far the most popular infant seat, if they'd "invested into" the Maxi Cosi system they just automatically went for the Pearl seat for the next stage, the 2Way Pearl came a bit later as well. I remember a lot of discussion and argument about ERF at this point, as well as impact shields being touted as an alternative - that was what I went for for my son in the end, because it was that much more affordable and portable to me as a non-driver.
Once Joie seats hit a wider market, this made a huge difference again as they were affordable. The Stages was indeed the first model they brought out and it just about fitted into that "reasonable" price bracket, they later had two models under £100. I honestly think this did a huge amount for ERF visibility and availability. Then the Joie 360 Spin (which I have listed as 2016) really transformed the market in itself. Spin seats were already popular but this made them affordable too. Suddenly everyone had one, and that is why I would put 2016 as the tipping point.