By reading some quotes (mainly from lannisters characters), it is imply the Valyrian Freehold was aware of a Western continent.
They built Dragonstone... Why ? Outpost ? Trading post ? Tyrion wondered why the valyrians didnt take hold on the land. 3 dragons and some footmen conquered a fair part of the seven kingdoms and destroyed armies of thousands men.
A rich land, scarcely populated, not unified into a single entity...
So the Valyrian freehold never attempted a war against Westeros.
But it could be inferred some trade existed.
1/ Valyrian steel
When Tyrion thinks about valyrian steel in ASOS, he pretend there is thousands weapons of it in the world. Hundreds in the 7 kingdoms.
He maybe wrong. After all, few valyrian steel weapons are shown.
But if there is really thousands of valyrian weapons... Some of them came into noble families far before the conquest. Longclaw is supposed to belong to the mormont family for 500 years.
So many of the valyrian swords in westeros were not given by Aegon as gifts to his vassals.
2/ The maesters.
The order of the maesters is supposed to date back before the conquest.
The word maester seems valyrian, since high valyrian and its dialect (from Bravosii to Dothraki) seems to favor such grammar (ae).
The citadel still owns some glass candles brought, allegedly, tohusands of years before the doom. When it burns, its rumored to be used as a communication device.
A maester who studied magic wears a valyrian steel link. After the death of the last dragon, magic was seen obsolete.
3/ Noble houses of valyrian ancestry.
It is said about to houses they have valyrian ancestries, being founded after the conquest. Velaryon and Baratheon.
House Dayne supposedly existed before the conquest, and many members of this house exhibit valyrian look.
Ok this post is all about speculation. Was the valyrian steel traded for fur in the north and gold to the west ? The Dayne family maybe descended from wine growers from Valyria who settled in Dorne?
The maesters : the vanguard for an invasion which never came? (not in the way it was planned)