block and beam subfloor airbrick issue

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1990s bungalow with an add on conservatory ( for summertime use ) to one end of back elevation. Bungalow has had cavity wall insulation retrofitted since. Subfloor airbricks(red plastic type) are on opposing sides to front and back (which are the longer elevations) only. 1 of these was venting into conservatory as floor was not raised to subfloor height of bungalow (never picked up by buyers survey in 1999 who just put that airbricks would ideally be on all 4 elevations). Bungalow has been handed down through family since. Subsequently had one additional subfloor airbrick (terracota brick type) added to side elevation of bungalow towards the back. The airbrick is positioned 500cm approx from corner end so that it presumably helps ventilate area of void where airbrick has been blocked. Building control advice sought over phone but not forthcoming as its not a recent build. Airbricks are positioned at second brick level above ground level. Have no idea whetehr these are the periscope type or not and cannot poke knitting needle through to ascertain due to integral mesh. However the additional airbrick enables knitting needle to go straight through to void. We are aware of an amount of powdery dry white substance which came out of a viewing hole during installation of said airbrick. We were able to ascertain that this was not the cavity wall insulation as originally suspected. The only comment made by the person checking cavity wall insulation was undisturbed was" is this a solid floor" (which we have subsequently learnt is what block and beam can be classed as). It was also noted that a DIY liner for the airbrick of some sort had been placed through the cavity wall. The brickwork is double thickness to above the level of the airbricks. Do we leave as it is/cover it over/look at its removal or block it off. One similar build on estate which faces same direction as ours has their airbricks on shorter side elevations only. Rest like ours, have them on long elvations only.
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One terracota airbrick has been placed into the side elevation of bungalow. No other airbricks exist along either side elevations. All subfloor airbricks are positioned along the front and rear elevations only. With the one which vents out from the subfloor void directly into the conservatory being blocked off, and being positioned towards the end of the rear elevation it seems the rationale for adding the odd airbrick was to compensate by ensuring there was still adequate ventilation of the block and beam subfloor void. Is this acceptable ? Apologies for diagram
l--[[--xx---------------]]--------- rear wall elevation--------
=
l-----aa ---bay window-------- front wall elevation ( aa indicates opposing airbrick)
a bay window area extends out at front
xx indicates blocked airbrick
[[ ]] indicates where add on conservatory sits along outside of rear wall
= indicates airbrick whiich has been added to side elevation to ventilate bungalow subfloor void
.withdrawal, NOT withdrawel ..bear with me, NOT bare with me
.definitely, NOT definately ......separate, NOT seperate
should have, NOT should of .....guaranteed, NOT guarenteed