Been watching this one with quite a bit of interest... yep, that was in 2007/2008 and measure using gas analysis in a lab. Timescale was first measurement in November and second in March. I was reasonably fit beforehand but training had been very sporadic and unstructured. The training during that period was predominately HR Zone 1-2 base work that, in theory, shouldn't have impacted massively on V02. However, I lost 8 kg of weight and, as CL has been saying, as kg is a factor in the score that would explain a large proportion of the increase.
Another factor is familiarity with the test protocol.. this was the third time I'd undertaken the test and, it's far easier with something to shoot for, however, you can't cheat the gas deflection point.
More significant in my point of view than the change in VO2 was a massive increase in economy (again shown by gas analysis) and the relationship between running pace and HR. I think too many people get obsessed by VO2 and, for the majority of distance runners, threshold as a percentage of VO2 and economy are better indicators of ability.... that said, when I was tested in September prior to my 2012 "A" race, mine was 72 ml/kg/min running and 75 ml/kg/min on the bike

... again though weight was down another 2 kg to 78 kg.
Anyway, what I've learned over the years is that many runners get to fussed about numbers and suffer from paralysis by analysis with regards to training. For the vast majority of non-elites it boils down to consistency in training. If you can do X3 runs per week and are training for typical fell races do:
1) LSD (long steady distance): Steady pace and relative to the distance that you typically race over. For example, if you tend to race for 40-60 mins, your LSD only needs to be 90-120 mins.
2) Tempo/Threshold: Sustainable discomfort... starting at 20 mins of effort and building up to 40 mins. Race pace work.
3) Hills/Intervals: Relevant to your races and/or addressing your weaknesses.
... anything more is really just window dressing. Make sure you recover properly and have an easier week every 3-4 weeks.
A final thought.. mainly for the long distance crowd. Many people will say,
"I need to run faster so, need to do speed work". Do you need to run faster or do you just need to not slow down? A subtle difference but a very important one that again returns to the importance of running economy.