I've been watching some Japan Open videos lately, and I came across this beautiful performance of Joannie Rochette in the 2009 event.
https://www.youtube.com/watch?v=KzxIv0iQhWA
At about 2:44, she does a combo which looks like a 3T-1Lo-3S. I watched other videos and saw that she did this for the whole season, and in the protocols, it is listed as a 3T+3S+SEQ. So I have two questions...
What she's doing there is not a half-loop (as Shayauki says). More like a little falling leaf followed by a right forward inside mohawk, which may be a bit hopped (hard to tell on the video).
1. Would the combo she did in the 2009-2010 season be considered a 3-1Lo-3 sequence today?
No, for the reason above -- it's not a 1Lo (with opposite-foot landing back outside back inside, i.e., half-loop) to between the triples.
Would all skaters be allowed to do this kind of sequence under the current system?
I think so, especially if that was an actual hop and not just a mohawk to get from RFI to LBI.
2. In the 2010 Japan Open, she does the 1Lo-3S sequence like the current skaters do it. And she did the same in the 2013 Japan Open as well, which seems to mean that she can no longer do the sequence like she did previously.
The rules for jump sequences have changed over the years.
What has been true of jump sequences since the beginning of IJS is that they can include "any number of jumps of any number of revolutions that may be linked by non-listed jumps and/or hops immediately following each other while maintaining the jump rhythm" and that the score is 80% of the two highest-value listed jumps in the sequence (if there are more than two).
What has changed somewhat is the definition of a sequence. At the very beginning it was allowed to do a step or turn between jumps and hops, but only one between each jump. That was later changed so that the skater must leave the ice with every turn and there can't be any strokes or edge changes between jumps, or else the sequence will either be called as the first jump only with the second one ignored, or if there are enough steps and loss of rhythm but it doesn't look like a mistake it could be called as two separate jump passes, which means the last jump pass of the program will not count at all.
(Also later an exception was explicitly added to allow a step from back outside landing edge to forward outside axel takeoff without a hop. And I think it is still allowed to change feet e.g. from a half loop back inside landing to a back outside toe loop takeoff and call it a sequence.)
So as of 2010, 3T-falling leaf-hopped mohawk-3S and 3T-half loop-3S both counted as 3T+3S+SEQ with a base value of 80% of the 3T plus 3S base values. So a skater could do whichever of those sequences was easier for her.
Then the rules for half-loop sequences changed. If the skater takes off directly from the half-loop landing into a salchow or flip, the element is considered a three-jump combo with the half-loop called as 1Lo, and full base value for all three jumps
It's still allowed to do either the 3T-falling leaf-hopped mohawk-3S (3T+3S+SEQ) or and 3T-half loop-3S (3T+1Lo+3S). However, the latter now earns significantly more points, so there's an obvious advantage to choosing the latter.
The only exceptions would be 1) if the skater has a much better success rate/higher quality with a sequence including half-revolution hops than with a half-loop combo or 2) the skater has a different three-jump combination s/he can do reliably with a higher base value than the triple-half loop-triple and wants to save the one allowed three-jump combo slot for the harder one.
So if the answer to question #1 is no, were there any other skaters who did the same sequence during the 2009-2010 season and had to change it in the 2010-2011 season just like Joannie did?
Offhand I can't think of anyone who did that specific sequence. But if they did, or something like it, the current rules would encourage them to do a true combination with half loop in the middle.