Numbering conventions as we’ve long understood them were set into place in 1973. There have been minor tweaks but the modifications that went into effect in 2021 are the most significant changes by far.
True dat … but those “minor tweaks” actually played a pretty big role for WRs and DLs …
Another change occurred in 2004, when the NFL allowed wide receivers to wear numbers 10–19 in addition to the 80–89 range; this was due to several NFL teams retiring 80-range numbers, as well as teams employing more receivers and tight ends in their offense.[3] Since 2010, defensive linemen are allowed to wear numbers 50–59; this is in part because of the interchangeability of linebackers and defensive ends (a defensive end in a 4–3 defense would be an outside linebacker in a 3–4 defense). In 2015, the NFL Competition Committee allowed linebackers to wear numbers from 40–49.[4]