Good research! I looked through the rankings,so overall: Liqin - 56 month on 1 spot (included 4 month besides this dite),Wanf Hao - 28 month.Thanks for posting that link to the this thread on Victor Barna Azlan.
Nobody in the modern era has surpassed Wang Liqin's 25 consecutive months as world #1. The ITTF world ranking history pages for Wang Liqin do not go back far enough to get the whole two years where he was ranked #1. I think it went from September of 2000 - September of 2002. But, he was also ranked #1 for all but 2 months between June of 2004 and February of 2007. If you just take the total # of months where he was ranked #1 and add them all together it is almost 5 years in the #1 slot. Hard to beat that in the modern era where, aside from his periods of dominance, the #1 rank seems to shift fairly regularly from one player to another.
Have you any info for pre-2001? For Waldner,Kong,Liu on 1 spot?