The obsession with the 1949 definition of veganism is unfortunate, as it ignores what we've learned about plastics in the last sixty or seventy years. "Synthetic" means "plastic". Plastics do not biodegrade and will be around for hundreds if not thousands of years after we're gone, harming the poor animals who will have to deal with the consequences of our consumerism. Every time you wash an acrylic sweater, bits of plastic end up in the laundry water and, eventually, in the bellies of birds and fish. Every time you buy a shoe made of "vegan leather" that falls apart after two months, you are unnecessarily adding plastic to the landfills. (Donating does not solve this problem; most donated clothing ends up in a landfill. When you buy second-hand clothing, you are diverting it from the landfill.)
Whether we like it or not, we all contribute to animal suffering by virtue of living in a society that sees animals as objects. The plants we eat come from farms that routinely kill animals like groundhogs and mice. In my mind, a vegan who, every few years, buys a wool sweater and a pair of leather shoes and uses them conservatively is a better vegan than one who mindlessly buys large amounts of synthetics. The latter may feel superior and label the former "not vegan", but he is not better for animals than the former.
Until we find a way to make plastics that are truly biodegradable, I think it is better to buy clothing only when absolutely necessary and choose, whenever possible, natural materials like cotton, linen, and wool, preferably used. I also believe it's important not to stop with the official definition of veganism but to do even more to help animals in the long run: avoid air travel; avoid plastics; buy as few things as possible; plant native plants and trees; and, last but not least, compost your compostable waste or encourage your municipality to establish a composting program. The list of things we can do is endless.
There was a recent New York Times article that argued, if I remember correctly, that cats and dogs eat a third of factory-farmed meat in the United States. It makes no sense that having a cat is "vegan" but buying the occasional wool sweater or leather shoes is "non-vegan". This focus on labels was what made me give up veganism after four months the first time I tried it (15 or 16 years ago) and is today a major factor that keeps me from being more active in the vegan movement. I don't want to go to a vegan festival and be kicked out because I'm wearing a wool sweater I bought years before I went vegan, and a pair of well-made leather shoes I've worn almost every day for years. If the vegan movement could be more conscious and accepting of how impossible it is to reduce animal suffering to zero in a world that is based on animal exploitation, it would grow much faster. The way to end animal suffering once and for all is not to label others as non-vegan or to endlessly argue about bugs, honey, wool and leather; it's to change our society to one that recognizes that it's not OK to abuse, torture, or kill animals. It is only when our society starts truly caring about animals that scientists will develop synthetics that are truly biodegradable, and we will be able to make choices that are truly animal-friendly.