The ancient Jews, including Moses, documented time differently than we do today. The Jewish year was based on lunar cycles (29.5 days), but a year was/is about 12.4 lunar cycles long. The Jews compensated for this by occasionally adding in an extra month, so the years were sort of shorter, but not enough to account for the incredibly long lives of the pre-flood peoples. (See more about the Jewish calendar here) So, I don't think there is any evidence of a severely shortened method of counting years, to answer your question.
However, the interpretation of what a year actually is has been questioned, some assuming a year is not to be taken literally. Even the personhood of the patriarchs has been questioned, some proposing that the patriarchs are actually eras of rule, or named nations.
Consider the following:
"What is the literal sense of a passage is
not always as obvious in the speeches and writings of the ancient
authors of the East, as it is in the works of our own time. For what
they wished to express is not to be determined by the rules of grammar
and philology alone, nor solely by the context; the interpreter must,
as it were, go back wholly in spirit to those remote centuries of the
East and with the aid of history, archaeology, ethnology, and other
sciences, accurately determine what modes of writing, so to speak, the
authors of that ancient period would be likely to use, and in fact did
use. For the ancient peoples of the East, in order to express their
ideas, did not always employ those forms or kinds of speech which we
use today; but rather those used by the men of their times and
countries. What those exactly were the commentator cannot determine as
it were in advance, but only after a careful examination of the
ancient literature of the East" (Divino Afflante Spiritu 35–36). -Pope Pius XII
Consider that the earth might have been very different preceding a worldwide deluge. We can't know what those conditions were, nor can we know how they impacted the longevity of human life. I've heard many theories on this, but I hesitate to discuss them here because I don't know how well-based they are on scientific evidence.
In addition, during those early days of humanity, the aging process might well have functioned very differently. The theories based upon the evolutionary process within our genetic history are very interesting. The late age at which these historical figures reproduced is notable--indicating a very different reproductive approach from what we know today. Many scientists in the field of study associated with the aging process see a strong tie between longevity and late reproduction.
Consider also that viruses and bacteria like we have today didn't exist in their current form during those days. Viral infections forever alter our DNA, and our children's DNA. That accumulates and alters us, potentially impacting our top end lifespan.
It could be a complex collection of influences, in conjunction with God's own will. It is an interesting field of study and, if these lifespans are really true, might contain some secrets we have yet to determine about how to prolong our lives today.
There is much out there that goes into depth with theories, and some are scripturally backed up. These are all theories with many suppositions and many real scientific objections. Exercise caution as you study.