Until mid-1984 EMC factory produced one model of a road bike, well-designed and well-made. Everything would be OK, but the competitors started to drive away, which Eddy Merckx never tolerated.
Counterattack was prepared elegantly and powerfully, unfortunately without taking into account the details. New materials were used (SLX, 753 - for the new flagship models, 501 - for the popular and cheaper model), the "narrow without SSC" version was invented, Silva "flat bottom" break bridge appeared, new BB cover MI 4 without chain bridge.
The production started at the beginning of the series (~ Z400 - or ~ summer / autumn 1984 ) for the 3-Athlete model and ... it is not known when for the Pro SLX and Pro 753.
... these are the minor details left out of the EMC plan...


- it is known that the "narrow" version appeared for sure ~ Z500; it is not known whether it concerned only the SLX / 753 version or was a "EM modified version" SL/531 prototype ( Gipiemme breake bridge "cube" ).
- the first confirmed Pro SLX "narrow" is ~ Z840 ( BB cover MI 4, break bridge Silva "flat bottom" )
- the first "mass occurrence" of Pro SLX and the appearance of Pro 753 is ~ Z2000... ok, problem?

The joke is that the Pro SLX did not have the X mark on the BB cover (the oldest confirmed Pro SLX with the X symbol is Z4330 - it is my frame by accident , and the Pro 753 never had any "its" mark ... I do not know the Pro SLX copy other than the Silva break bridge ... which does not mean they were not made; for sure there was a series (first) Pro 753 with break bridge ... Gipiemme "cube", no different (except for stickers and weight) ... from "EM late version". In the beautiful red-white-red colors of TeVe Blad team 1985 ...
In the later Pro SLX and Corsa Extra, " lack of X" epidemic did not die out - all the time the surest way to check the SLX remains to examine the tubes entering the BB cover ... rifling? ok.
Pro SLX changed in Corsa Extra imperceptibly (without changes in construction) ~ Z8000.
t.b.c.