David,
Yes, of course, you are right. Both types of markings and camouflage schemes were used on the Polish Armed Forces Chevrolet ambulances. One of them is classic military scheme with two-tone camouflage and simple red cross symbol as can be seen at your pic. The other one is smooth olive drab scheme with more civilian markings where the red cross symbol is encircled by two-language inscriptions: "Polski Czerwony Krzyż" and "Polish Red Cross". If I am not mistaken this second scheme is more typical for the ambulances donated by various organizations. For example 10th Armoured Cavalry Brigade of the Polish 1st Armoured Division had such an ambulance founded by the Chicago-based Legion of Young Polish Women.
Best regards
C.
