Then maybe it sold less on the previous years. 

One thing people here don't seem to grasp is the fact that for Electronic Arts, "install base" is not the same as "consoles sold".
Install base for EA gives them an estimate of how many customers are available to sell software to. We can safely assume that EA thinks (and I think that this is a reasonable assumption), that XBox1 X sales went almost entirely to Old-XBox1 owners. Hence while the number of consoles sold increases, the install base does not. They also neglect the "trickle down" effect of old consoles sold by new X1X owners into the secondary market over time (generating an increasing install base).
In the end Electronic Arts' "install base" logically is lower than "actual consoles sold", likely by a few millions. So unfortunately, this EA statement is no secret path to get to the "precise" sell-through numbers for XBoxes.

You are so right install base is different to consoles sold 

so you are saying EA thinks every ps4 pro sold was sold to a new customer? Its the only way the numbers make sense then. 

Good thing I know what I'm talking about.

It's much more likely that it is simply a bad estimate. There are two ways how EA can estimate:

1. Consoles sold - Here the numbers don't add up because ZhugeEX said that Xbox One was "around 35m" by the end of 2017. The real number is around 108-109m, therefore EA made a bad estimate.

2. Installed base as you say, so PS4 Pro and Xbox One X sales do not count towards the total - While this could explain the estimate of 103m by the end of 2017 (PS4 below 70m, XB1 ~34m for a total of 103m), it leaves the question how PS4 and XB1 are supposed to combine for 27m units in calendar year 2018. That's a number these two consoles cannot possibly reach if PS4 Pro and Xbox One X sales don't count towards installed base, so once again, the conclusion has to be that EA made a bad estimate.

I can't believe this myself but Bishopti (once a mod and insider on GAF) has said these figures are accurate.

ZhugeEX:

"I'm not sure what the reason is for the discrepancy with EA's estimates.

It could be it excludes Pro/One X numbers.
It could be that EA excludes a territory like Japan (they used to do this last generation)
It could be that EA estimates PS4 at a lower number. (Which would be weird given Sony release the official numbers)
It could be that installed base =/= sell through in EA's eyes. So replacement consoles sold wouldn't count and only people actively using consoles would count?

EA's estimates aren't wrong. I'm just fairly certain one of the above things is true.

Ultimately what we do know is PS4 sell through was 73.6m at the end of 2017. Xbox One is less than half of that total which shows the big gap between the two in terms of sales. But that's something that has been known for a long time."

^ this could be a explaination right?

If we ignore PS4 + XBO sales in japan, do the numbers EA supplied make sense?

I really doubt it's that low. NPD has the Xbox One over 8 million these past two years. If these numbers are true, that would mean the Xbox one sold around a million units per year outside the US. Yeah, this doesn't adds up whatsoever.

I do wonder how ZhugeEX has all the numbers to be able to give an accurate sell through (or were his numbers shipped?) We already have Japan's numbers thanks to Media Create, and we know he gets NPD numbers. We do have a tracker for much of EU, but not sure if he actually gets those numbers. Where does he get the others? Could it be that his estimates for those not tracked are overestimated. Personally, I would believe a huge partner like EA, since they undoubtedly get most of the info, and probably talk to MS themselves about consoles shipped/sold when preparing to make a marketing deal.