Post 2016 all MAX3421 are version 3 Prior to 2016 some ICs are die version 3. Those are marked with 3 as below: MAX3421EE YYWW 3 (YY-> Year, WW-> Workweek (0 to 52), example for 2016, YY = 16) OR MAX3421EETJ YYWW 3 Source: MAX3421 Errata, Document ID No. 19-0647; Rev 2; 4/16
Note: The version of the MAX3421E can be determined electrically (by firmware) by reading the Die Version register (R18); e.g., 0x01 is version 01, 0x12 is version 02, 0x13 is version 03. The die may also be discovered by reading the top mark as described below.