That's true.
Have a look at previous releases:
iPhone 4 - A5 - Sept. 2011
iPad 2 - A5 - Mar. 2011
iPad 3 - A5X - Mar. 2012
iPhone 5 - A6 - Sept. 2012
iPad 4 - A6X - Oct. 2012
iPhone 5S - A7 - Sept. 2013
iPad Air - A7 - Oct. 2013
iPhone 6 - A8 - Sept. 2014
iPad Air 2 - A8X - Oct. 2014
iPhone 6S - A9 - Sept. 2015
iPad Pro - A9X - Nov. 2015
iPhone 7 - A10 - Sept. 2016
iPad "2017" - A9 - Mar. 2017
iPad Pro 2 - A10X - June 2017
iPhone 8 - A11 - Sept. 2017
Apple have had a pretty consistent schedule of releasing iPhone's with their new chip followed by iPad's with "X" variant chips a month later. This is true for all except the introduction of the iPad 2, iPad 3 and iPad Air.
It's quite possible that we'll see Apple:
a) Quietly update the iPad Pro with an A11X after the iPhone X release or
b) Prolong iPad Pro 2 life cycle until October 2018, potentially skipping A11X and going to A12X (or even A12 like they did with the iPad Air's A9) or
c) Stick to a yearly update and release new iPad Pro's with A11X in June.
I suppose it all really depends on how well they sell and how Apple want to position their Pro line.