Well a quick look at apples spec sheets would have shown you immediately what the score is for both versions.
2012
- Intel HD Graphics 4000
- NVIDIA GeForce GT 650M with 1GB of GDDR5 memory and automatic graphics switching
- Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, at millions of colors
Thunderbolt digital video output
- Native Mini DisplayPort output
- DVI output using Mini DisplayPort to DVI Adapter (sold separately)
- VGA output using Mini DisplayPort to VGA Adapter (sold separately)
- Dual-link DVI output using Mini DisplayPort to Dual-Link DVI Adapter (sold separately)
2013
- Intel Iris Pro Graphics
- NVIDIA GeForce GT 750M with 2GB of GDDR5 memory and automatic graphics switching
- Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, both at millions of colors
- Thunderbolt digital video output
- Native Mini DisplayPort output
- DVI output using Mini DisplayPort to DVI Adapter (sold separately)
- VGA output using Mini DisplayPort to VGA Adapter (sold separately)
- Dual-link DVI output using Mini DisplayPort to Dual-Link DVI Adapter (sold separately)
- HDMI video output
- Support for 1080p resolution at up to 60Hz
- Support for 3840-by-2160 resolution at 30Hz
- Support for 4096-by-2160 resolution at 24Hz
So to make it simple officially no you can't support 3 external screens, in practice you can with splitters and USB connectors but the performance may be somewhat poor.
Edit just noticed your other machine is the early 2013 it's no different t your 2012