Although medieval cathedral construction plans did often have timelines of roughly a century. The reconstruction of Notre Dame in Paris is expected to be 20–40 years which puts it awfully close to the 2070 completion date as well.
Quite a turn of events that made it possible to resume that building after the original plans were found, here is the summary i found:
> In the 1790s, when the French Revolutionary Army drew close to Cologne, the
Cathedral treasures were removed for safekeeping. These included the plans and
drawings for the west front, which were transported with other items to Amorbach and
eventually lost and forgotten. In Amorbach, the large “F-Plan” was used by a family for
some time to dry beans, and later wrapped around their son’s new suitcase to protect it
as he traveled to the university in Darmstadt. It was in Darmstadt, in the attic of the inn
where the son arrived that the Plan was rediscovered and recognised by G. Moller as
the missing drawing of the west front.
Most of those are a continuous project. The islands are the ultimate destination for incinerator ash and large garbage. The occasional tunneling project will dump the dirt etc.
You can see from goog maps how there are a couple outline online islands under "construction" and once those are filled they'll outline more.
https://en.m.wikipedia.org/wiki/Sagrada_Fam%C3%ADlia