The mystery v99999 is an artifact of how older releases of the p4 command line client set the protocol level. In the code, it looked something like this:

client.SetProtocol( "api", "99999" );


In the absence of better version information, the server logs the API protocol level, or if that's not set, the client protocol level. Since 2004.2 p4 always sets the API level to 99999, so it's a version of p4 that was built after that, but before they introduced an explicit version string (2005.2). So basically if you see v99999 it's either a 2004.2, or 2005.1 p4.

reference:
kb.perforce.com/article/512