You are right. This is missing both in the documentation and cli output.
I expanded my test a bit and it's version 5 it's sending:
[root@space-XXXX ~]# tcpdump -vvvvvni eth0 port 6343
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
20:48:25.390592 IP (tos 0x0, ttl 255, id 288, offset 0, flags [none], proto UDP (17), length 272)
X.X.1.5.50035 > X.X.1.110.sflow: [udp sum ok] sFlowv5, IPv4 agent X.X.1.5, agent-id 16, seqnum 288, uptime 1213994542, samples 1, length 244
flow sample (1), length 208,
20:48:32.104573 IP (tos 0x0, ttl 255, id 289, offset 0, flags [none], proto UDP (17), length 296)
X.X.1.5.50035 > X.X.1.110.sflow: [udp sum ok] sFlowv5, IPv4 agent X.X.1.5, agent-id 16, seqnum 289, uptime 1214001257, samples 1, length 268
counter sample (2), length 232,
I will push information back that documentation and feature explorer should be updated to reflect this.... but no promises about it being fixed.