Korchnoi's Career 1945-1977, Three Views

Two weeks ago, in Korchnoi's Career 1945-1977 (on Paper), I extracted an index of Korchnoi's games for the period 1945-1977 from the book 'Korchnoi's Chess Games' by Levy & O'Connell. Last week, in Korchnoi's TMER 1976-2000, I compared games for the period 1976-2000 from two PGN collections compiled around the turn of the century -- one by UPITT and one by GMchess.

Of course, the two PGN collections also include games going back to 1945. How do these three sources, a book and two files, compare in their coverage of Korchnoi's pre-1978 period?

The chart on the left shows a count of games played in a given year for each of the three sources, plus an average of the three sources. For any particular year, the counts are roughly equivalent.

How does the data compare for a specific year? The following table shows events for the year 1977 from the three sources.

Src	Yr	Venue	Ct
L&O	1977	*KL	1
L&O	1977	*KS	1
L&O	1977	KS	1
L&O	1977	LEE	13
L&O	1977	MTX	9
L&O	1977	xKP1	12
L&O	1977	xKP2	13
L&O	1977	xKS	17
GMC	1977	Montreux (Switzerland)	10
GMC	1977	Netherlands	2
GMC	1977	Zurich (Switzerland)	3
GMC	1977	Ch Germany (team) (South-west) 1977/78 * Germany	1
GMC	1977	Ch Netherlands * Leeuwarden (Netherlands)	13
GMC	1977	Ch World (match) (cand.) (1/2) * Evian (France)	12
GMC	1977	Ch World (match) (cand.) (1/4) * Ciocco (Italy)	13
UPI	1977	Belgrade cm f	17
UPI	1977	Ciocco cqf ,CAND	4
UPI	1977	Evian cm sf	12
UPI	1977	Il Ciocco cm qf	8
UPI	1977	Leeuwarden NED ch	11
UPI	1977	Montreux	10

While the data again looks comparable, it's only because I eliminated 75% of the 'events' for UPITT, where the PGN headers haven't been standardized. Even for the six remaining events, Ciocco and Il Ciocco identify the same Candidates match.

To make progress for the period 1945-1977, I need to work only with the Levy & O'Connell material (on paper) and the GMchess data. The UPITT data can be ignored for now.