Apologies, I mentioned 'SECAM' which for me stands for 'France's own television system' but I understand it might not follow that easily for people not versed in the subject. I have to correct you that it's wasn't 'the usual' system, that was in fact 625 lines, an adaptation of the German system that ended up as the standard. 819 was only used for the (original) first channel in France, Belgium and Monaco. When the secondary channels started they all opted for 625 instead, and when color was implemented it used it too. The main drawback of the original French implementation was the wildly higher required bandwith (roughly three times that of a regular channel) and secondary that the audio signal was on the other 'side' of the video signal. This meant that when allocating the frequency spectrum to individual channels, it caused an extra loss of space because the 'odd' 819 channel didn't occupy the usual reserved space for its audio channel and did occupy an extra part instead, blocking another channel from being placed right after it (tv channels are spaced on fixed intervals) .
The third drawback that put the final nail in the coffin was that the color tv's introduced in the mid-60s had a lower absolute resolution, because they featured three groups of separately colored dots (the red, green and blue ones we all know) with a
shadow mask. Basically a plate with holes (later wires in Sony's Trinitron) instead of one group of white dots without a mask that display B/W television. That also caused all B/W signals, including 819, to be displayed in effectively 625ish quality or less and thus it left no effective use for the format anymore (let alone it didn't feature color obviously).
Back on-topic, I would be very doubtful that a 819 line recording of the Paris concert exists somewhere. Ampex recorders in use by RTF did support it, but this was 9 out of 10 times used for regular delayed broadcasting (recording a show during working hours, broadcast it at night / on the weekend and optionally a rebroadcast on a later date). For archival footage it would feature regular 625 line recording as otherwise it wouldn't be portable to any other form of broadcasting. I have to say I've never observed *any* 819 line archival recording and I'm not sure INA or some other French archival institute even feature those recordings.
