According to Digikey, some at-tinys are designed to work up to 5.5V, (ex attiny44A), while others indicate rating to 3.6V (some attiny44V, though not all). The 5.5V tiny44V's reference a datasheet that is plain tiny44 (neither
"A", nor "V").
In any case, even the 3.6V tiny44v's indicate an absolute damage limit of 6.0V...so does that mean they are usable in 5V circuits? It would seem so, unless some critical analog level was at stake. Is the lower rating merely to provide specific operating data at 3.6V---but then why not simply include that in the normal 5V datasheet? Some 5V boards were apparently built using 3.6V parts & there have been programming issues (the question is, is it due to these parts, or something else). Some parts have mysteriously failed (can no longer connect), though they seem to be running the prior code.