'Official statements' lmfao. You can use the tiers as a guide, but when has Lucas actually adhered to them? Let's look at the fights from Lucas' point of view, keeping in mind his limited understanding of combat (things like Vaapad, the interplay between styles, different tactics etc.)
Mace Windu vs Darth Sidious
Mace: Tier 8 - Sidious: Tier 9
Winner: Mace/Draw
Obi-Wan vs Anakin Skywalker
Kenobi: Tier 8 - Anakin: Tier 9
Winner: Obi-Wan/Draw (They were equals)
Count Dooku vs Obi-Wan Kenobi and Anakin Skywalker
Kenobi: Tier 8 - Dooku: Tier 8 - Anakin: Tier 9
Winner: Early on Dooku, Later on Anakin.
I could go on and on. There have been reasons (more like ridiculous rationalisations) given for these instances, but it's stupid to suggest that George had them in mind. Do you honestly think that if Lucas had Mace on the tier below Sidious, the reason in his head for the Windu victory/draw would be thanks to some dark-side channelling lightsaber style? Also, the Count isn't an 8 bordering on a 9 like Mace, and the gaps between tiers are huge. Yet Lucas was happy to show Dooku easily outmuscling the duo on two occasions, flooring and later ragdolling Kenobi, kicking Anakin across the room etc. Doesn't seem like he's adhering to these 'levels.' Tell me with a straight face that by Kenobi getting ragdolled, the intent wasn't to show us; Dooku >> Obi-Wan, but instead that the latter was just caught off-guard in the middle of combat like a ****ing retard? Was that really Lucas' line of thought? Of course not.
Point is; The tiers exist, fine. But Lucas doesn't care about them, as anyone can beat anyone based on circumstance/need of the plot.