Has the '5' key on the numeric keypad ever had an alternate function in hardware?

I looked at my library of images, and found two examples that seem relevant.

1:

that seems to be using the numeric 5 for… something related to cursor manipulation. I am not sure what it does.

2:

with a trackpad built into it. It seems that the numeric keypad doubles as hardware “mouse keys”, with extra arrow keys and 5 labeled as “Click.”

The special function "printed" on the '5' on the numeric key pad was (and still often is) a mark to recognize that key with your fingers without looking at it.

There is an odd variant of USB numeric keypad, VZTEC VZ-UK2151, which had numeric key '5' as function key 'Tab'. See the following screenshot (bottom-left: enlarged image of the key) as proof.

That 5 key works same as Tab key. It also works in GNU/Linux, even not listed as supported operating system besides Windows and Mac OS X. The product was likely manufactured in 2011.