"hallis"
But you get the concept..if it happens today then it happened then. I recently saw an article about how the Spartans may have been gay.
It's common knowledge to historians and classical scholars that the Spartans encouraged homosexual relationships with younger men, although being exclusively gay was seldom a viable option (the older lover was expected to help in selecting a wife for the younger). This isn't information that was at any time lost or unknown, but you're right in that historians at different times placed different emphasis at such things. For example, if you read decent translations of ancient Greek works, you'll find (for example) that their plays commonly had sexually explicit humor, and even the highbrow cogitations of Socrates are sometimes sprinkled with a homoerotic image or two. Older, esp. Victorian-era, translations tended to either mangle the text with obfuscated imagery at those points and provide footnotes in a completely different language, usually Latin, but sometimes others (like Italian), so that the delicate sensibilities of the readers would not be harmed.
In what sense do you think we are not "being told everything"? Sure, in the trivial sense, it's completely true--when a historian or classical scholar writes a book, he or she won't include "everything" from the original sources. If you mean that he or she may have some personal bias and (perhaps subconscious) agenda when they interpret those sources, that's also true. And the sources themselves may have questionable accuracy--this is the case not just for ancient history, but even yesterday's newspaper articles. This is particularly problematic for ancient history, however, since so much has been lost that any possible contrary sources have been lost (unlike more modern articles), and also complicated by simply different factual standards. For example, Herodotus wrote that over a hundred thousand slaves worked on the great pyramid, whereas modern analysis shows maybe twenty to thirty thousand. But it's probably not his fault--he recorded hearsay long after the fact.
So yes, regarding the past we see though a glass darkly, but overall this seems to be not a matter of being "not told everything" (by whom?), but rather there not being enough information in the first place.