A note about building a discrete equivalent of the classic LM3909 prompted me to measure some 2N3904 and 2N3906 transistors:

The DC gain and VBE for each flavor look comfortingly uniform:

Quite unlike those Hall effect sensors, indeed.
Most of the VBE variation comes from temperature differences: re-measuring the 2N3904 transistors with VBE ≅ 672 mV put them with their compadres at 677 mV.
The 2N3906 transistors have wider gain and VBE variations, so selecting a matched pair for the LM3909 current mirror makes sense.
The sheet inside the lid collects some essential parameters for ease of reference:
Class Type VCE IC HFE 1 2N2222 GP NPN 40 600 100 2 2N3904 LP NPN 40 200 100 3 2N3906 LP PNP 40 200 100 4 2N5401 HV PNP 150 600 60 5 2N5551 HV NPN 160 600 80 6 A1015 OSC PNP 50 150 70 7 C1815 OSC NPN 50 150 70 8 C945 GP NPN 50 150 70 9 S8050 PP AMP NPN 40 500 120 10 S8550 PP AMP PNP 40 500 120 11 S9012 PP AMP PNP 40 500 64 12 S9013 PP AMP NPN 40 500 64 13 S9014 LN LF NPN 50 100 280 14 S9015 LN LF PNP 50 100 200 15 S9018 VHF OSC NPN 15 50 100
You’re welcome.