Yes, you're right. Emilius Alphonsus was born to the unmarried Florentia in 1872. She married Henricus in 1881. At that time Emilius became 'legitimate'.
Dutch text
Het kind waarvan
den akte van geboorte hier-
nevens is erkend en ge-
wettigd geweest door het
huwelijk van zijne vader en
moeder Henricus Deside-
rius Versaevel en Florentia
Emerentia Legrand aange-
gaan voor den ambtenaar
van den Burgerstand der
Stad Ypre, den 22 Augusti 1800
één en tachtig.
De Greffier der Rechtbank
... TybergheinTranslation
The child mentioned on the birth certificate is acknowledged and legitimized by the
marriage of his father and mother,
Henricus Desiderius Versaevel and Florentia Emerentia Legrand,
entered before the civil registrar of the City of Ypres, on the 22nd of August, 1881.
The Clerk of the Court,
... Tyberghein
Wedding certificate of the parents:
https://agatha.arch.be/data/images/513/513_9999_999_1982926_000/0_0299