I can’t be sure how inaccurate your first test was but I remain dubious that it gave you what you needed. This new test does look like good data and the cross over is pretty in line with what we would expect with someone who’s done 4 months of base training. While your gain is on the high side its not out of the question if you were doing a high volume of the base training. You may also be a fast responder. People training response/adaptability fits a bell shaped curve largely due to genetics.
Do you have some old course you used to do with regularity? Like a hill climb or running loop. You can do a performance test and compare how fast you are on the same course at the same HR. Performance gains are really what we after in the end anyway.