Only advance diseases have a limit

code/datums/diseases/_disease.dm

@@ -42,10 +42,8 @@
 
 //add this disease if the host does not already have too many
 /datum/disease/proc/try_infect(var/mob/living/infectee, make_copy = TRUE)
-	if(infectee.diseases.len < DISEASE_LIMIT)
-		infect(infectee, make_copy)
-		return TRUE
-	return FALSE
+	infect(infectee, make_copy)
+	return TRUE
 
 //add the disease with no checks
 /datum/disease/proc/infect(var/mob/living/infectee, make_copy = TRUE)

code/datums/diseases/advance/advance.dm

@@ -56,13 +56,13 @@
 	return ..()
 
 /datum/disease/advance/try_infect(var/mob/living/infectee, make_copy = TRUE)
-	var/replace_num = infectee.diseases.len + 1 - DISEASE_LIMIT
+	//see if we are more transmittable than enough diseases to replace them
+	//diseases replaced in this way do not confer immunity
+	var/list/L = list()
+	for(var/datum/disease/advance/P in infectee.diseases)
+		L += P
+	var/replace_num = L.len + 1 - DISEASE_LIMIT
 	if(replace_num > 0)
-		//see if we are more transmittable than enough diseases to replace them
-		//diseases replaced in this way do not confer immunity
-		var/list/L = list()
-		for(var/datum/disease/advance/P in infectee.diseases)
-			L += P
 		sortTim(L, /proc/cmp_advdisease_resistance_asc)
 		var/datum/disease/advance/competition = L[replace_num]
 		if(totalTransmittable() > competition.totalResistance())