The reason that Alt+Num16 gives you ►, while Alt+Num016 gives you nothing, is so you can access both the characters that are mapped to codes 1 through 31 by IBM PC code page 437 and the control characters in that range of ASCII. You enter a leading zero for the control characters and omit leading zeros for the graphic characters in this set: ☺☻♥♦♣♠•◘○◙♂♀♪♫☼►◄↕‼¶§▬↨↑↓→←∟↔▲▼
To give this a try, you can type Alt+Num9 for ○ (circle) or Alt+Num09 for Tab and Alt+Num13 for ♪ or Alt+Num013 for Return. Let's just say that the use for ASCII 16 (Ctrl-P) is lost in the mists of time.
If you are using a Unicode-compatible application such as Wordpad, entering Alt+Num225225 is the same as Alt+Num28617 (225225 % 65536 = 28617) which is character U+6FC9 or 濉