Interesting post from the Sage City community regarding X3 and support only being offered for current and one prior release. While Sage haven't said as much - this is pretty much the same policy they are carrying out with Sage 100 by only offering product updates for the current and one prior version.
https://sagecity.na.sage.com/support_communities/sage_erp_x3/b/sageerp_x3_product_support_blog/archive/2016/12/08/sage-x3-support-changes-coming-in-2017