Important for the question is Revelation 20:1-7, where different periods of one thousand years are mentioned; without it being super clear when they start or what will happen. Now these thousand years can of course be interpret symbolically, as was for example done by Augustine in City of God (from 426AD), but can also be interpret literally and importantly can be interpreted as having started with the crucifixion. Hence, there exists reason to believe that people did not just "commemorate" it, but saw it as much more important than that.

Two common suggestions for people taking note of the year are the vast amount of churches constructed leading up to the year 1033 and the so called "Peace of God".
Regarding the church constructions so is Rodulfus Glaber, French monk who lived at the time, usually quoted as he claimed that there was a "white mantle of churches" being built and that these churches were being built despite that the churches that already existed where "properly built and not in the least unworthy". This flurry of church construction is rather odd, but as it happened in the years leading up to 1033 is it often explained as being a reaction on the end of the potential thousand year period; you can read more about it here.
Regarding the "Peace of God" so was it a movement started in the late 10th century by churches in order to protect the clergy, women, pilgrims, and generally civilians from violence. And quoting Encyclopedia Britannica:

The apocalyptic character of the movement is confirmed by the high percentage of peace meetings that occurred in the decade before 1000 and again just before the year 1033, which was thought to be the 1,000th anniversary of the death, Resurrection, and Ascension of Christ. The council of Bourges bears witness that the hope of direct heavenly intervention was giving way to earthly arms bearing after the passing of the apocalyptic years.

(Final side note, as far as I am aware are the most commonly suggested years for the crucifixion 30-33, not 33-36)