CEA and CA 19 9 increases in colon cancer with liver met.

My dad (61 years old) was diagnosed with stage 4 colon cancer with liver met. more than a year ago. He had 8 chemo treatments after his colon surgery, and then he had 2/3 of his liver taken. After his liver surgery, he had another 3 chemo treatment to prevent recurrence. At the end of the chemo, he had PET/CT and they were fine. His CEA was 3.8 and CA 19 9 was 37. Just a month later, he had another blood test (not because our doctor asked for), and his CEA and CA increased to 4.7 and 43. I know that these values do not reveal anything for sure, and may increase due to various reasons, but do you think the increase in both values shows a recurrence? It has been less than 2 months since he stopped chemo treatment.  
Also, he smoked heavily for 30 years, but he hasn’t for last 6-7 months. Do we need to consider 3 or 6 as a normal limit for CEA tests? Thanks so much in advanced.