https://www.quora.com/What-are-the-main-differences-between-Bluetooth-4-0-4-1-and-4-2-in-the-Layers-Baseband-LMP-L2CAP-app-Layer
http://sina.com.hk/news/article/20131223/0/5/0/-38766.html?cf=o.digital
The difference between BLE4.1 and BLE4.0 is:
1) Coexist with 4G networks to reduce interference
2) Can be the master and slave at the same time, providing speed
3）ipv6
4) Simplify the connection process of the device
V4.0 to V4.1 hardware does not need to be changed.
The difference between BLE4.1 and BLE4.2:
http://www.semiconductorstore.com/blog/2015/BLE-4-2-vs-BLE-4-1/1548
Key Bluetooth 4.2 Features Not Available with Bluetooth 4.1
IoT Capabilities:
Low-power IP (IPv6/6LoWPAN)
Bluetooth Smart Internet Gateways (GATT)
With BLE 4.2 Bluetooth Smart sensors can transmit data over the internet.
Security:
LE Privacy 1.2
LE Secure Connections
With new, more power efficient and highly secure features, BLE 4.2 provides additional benefits allowing only trusted owners to track device location and confidently pair devices.
Speed:
250% Faster
10x More Capacity