Look at the Nihon Ki-in records of the World Amateur Go Championships.
A typical SGF2 file starts(; SZ GN[The 28th WAGC Round6] DT[2007/05/30] PC[Tokyo NihonKiin] PB[KUIN(NED] PW[BAZYNSKI(POL] KM[6.5] RE[B won by resign.] ;B[pc] ...
Differences are:( TE[The 29th WAGC Round 1] RD[2008.5.28] PC[Nihonkiin, Tokyo] TM[1 hour 30 minutes] LT[10/15 Canadian byo-yomi] KO[6.5 pts] RE[White won by resign.] PB[Leon MATOH] BR[27-SVN] PW[Frank JANSSEN] WR[7-NED] GK ;B[pd] ...
(i) The start is ( instead of (;. This means that some SGF readers won't find any game in an SGF2 record.
(ii) Some properties have different names. Mainly:
SGF SGF2 meaning GM GK game (go) DT[..] RD[..] date EV[..] TE[..] event KM[..] KO[..] komi OT[..] LT[..] overtime, byo-yomi HA[..] HD[..] handicap (with built-in AB)
In SGF the property TE is found as TE, tesuji; KO is found as KO, illegal move (gnugo uses IL); LT is found in SGF FF as LT, loss on time is enforced.
HD sometimes implies AB[dd][dp][pd] and sometimes AB[dp][pd][pp].
(iii) SGF files usually are in ASCII or UTF-8 (sometimes with a CA property indicating the character set). SGF2 files usually are in ASCII or CP932 (SJIS).
Games in SGF2 format are also found e.g. on baduk.lg.co.kr and www.cyberoro.com. Occasionally one sees traces elsewhere, like RD instead of DT in an otherwise regular SGF file, or both GK and GM in the same file.
I don't know who invented this format, or why it is useful.